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Purpose

In this paper, the author defines the function B¯i,jδ,k(n), the number of singular overpartition pairs of n without multiples of k in which no part is divisible by δ and only parts congruent to ± i, ± j modulo δ may be overlined.

Design/methodology/approach

Andrews introduced to combinatorial objects, which he called singular overpartitions and proved that these singular overpartitions depend on two parameters δ and i can be enumerated by the function C¯δ,i(n), which gives the number of overpartitions of n in which no part divisible by δ and parts ≡ ± i(Mod δ) may be overlined.

Findings

Using classical spirit of q-series techniques, the author obtains congruences modulo 4 for B¯2,48,3(n), B¯2,48,5 and B¯2,412,3.

Originality/value

The results established in this work are extension to those proved in Andrews’ singular overpatition pairs of n.

For |ab| < 1, Ramanujan's general theta function f(a, b) is defined as

(1.1)

where the product representations arise from Jacobi's triple product identity [1, p. 35, Entry 19].

(1.2)

Throughout the paper, we use the standard q-series notation, and fk is defined as

The special cases of f(a, b) are

(1.3)
(1.4)

and

(1.5)

A partition of a positive integer n is a nonincreasing sequence of positive integers whose sum is n. An overpartition, introduced by Corteel and Lovejoy [2], of a nonnegative integer n is a nonincreasing sequence of natural numbers whose sum is n in which the first occurrence of a number may be overlined.

Recently, G. E. Andrews [3] defined combinatorial objects, which he called singular overpartitions and proved that these singular overpartitions depend on two parameters δ and i can be enumerated by the function C¯δ,i(n), which gives the number of overpartitions of n in which no part divisible by δ and parts ≡ ±i (mod δ) may be overlined. The generating function of C¯δ,i(n) is

(1.6)

He also proved that

(1.7)

Andrews [3] proves that, for all n ≥ 0, C¯3,1(n)=A¯3(n), where A¯3(n) is the number of overpartitions of n into parts not divisible by 3. The function A¯(n), which counts the number of overpartitions of n into parts not divisible by , plays a key role in the work of Lovejoy [4].

Chen et al. [5] have generalized (1.7) and proved some congruences modulo 2, 3, 4 and 8 for C¯3,1(n). They also proved some congruence for C¯4,1(n), C¯6,1(n) and C¯6,2(n) modulo powers of 2 and 3. More recently, Ahmed and Baruah [6] have found some new congruences for C¯3,1(n), C¯8,2(n), C¯12,4(n), C¯24,8(n) and C¯48,16(n) modulo 18, 36. Chen [7] has also found some congruences modulo powers of 2 for C¯3,1(n), C¯4,1(n). Yao [8] has proved congruences modulo 16, 32, 64 for C¯3,1(n). Naika and Gireesh [9] have found some congruences modulo 6, 12, 16, 18, 24, 48 and 72 for C¯3,1(n). Naika and Nayaka [10] have proved some congruences for CO¯3,1(n) modulo powers of 2 and 3. They have also proved in a paper [11] modulo 4 for C¯4,13(n) and C¯4,15(n).

In [12, 13], Naika et al. have defined the Andrews' singular overpartition pairs of n. Let C¯i,jδ(n) denote the number of Andrews' singular overpartition pairs of n in which no part is divisible by δ and only parts congruent to ± i, ± j modulo δ may be overlined. Andrews' singular overpartition pair π of n is a pair of Andrews' singular overpartitions (λ, μ) such that the sum of all of the parts is n. They also established Ramanujan-like congruences for A¯1,26(n) modulo 3,9, 27 and infinite families of congruences for A¯1,512(n) modulo 4, 6 and 9.

In this paper, we define the function B¯i,jδ,k(n), the number of singular overpartition pairs of n without multiples of k in which no part is divisible by δ and only parts congruent to ± i, ± j modulo δ may be overlined. The generating function of B¯i,jδ,k(n) is given by

(1.8)

In this paper, we establish some congruences modulo 4 for B¯2,48,3(n), B¯2,48,5 and B¯2,412,3. The main results of this paper can be stated as follows.

Theorem 1.1.

For all integers α ≥ 0 andn ≥ 0,

(1.9)
(1.10)
(1.11)
(1.12)
(1.13)
(1.14)
(1.15)
(1.16)
(1.17)
(1.18)
Theorem 1.2.

Let p be a prime ≥ 5,6p=1. Then for all integers α ≥ 1, and n ≥ 0,

(1.19)
Theorem 1.3.

Let p be a prime ≥ 5,6p=1. Then for all integers α ≥ 0, and n ≥ 0,

(1.20)
whereiis an integer and 1 ≤ i ≤ p − 1.
Theorem 1.4.

For all integers α ≥ 0 andn ≥ 0,

(1.21)
(1.22)
Theorem 1.5.

For any prime p ≥ 5,α ≥ 0 andn ≥ 0, we have

(1.23)
Theorem 1.6.

For any prime p ≥ 5,α ≥ 0,n ≥ 0 and l = 1, 2, …p − 1, we have

(1.24)
Theorem 1.7.

For all integers α ≥ 0 and n ≥ 0,

(1.25)
(1.26)
(1.27)
(1.28)
(1.29)
(1.30)
Theorem 1.8.

For any prime p ≥ 5,α ≥ 0 and n ≥ 0, we have

(1.31)
Theorem 1.9.

For any prime p ≥ 5,α ≥ 0,n ≥ 0 and l = 1, 2, …p − 1, we have

(1.32)

We need the following few dissection formulas to prove our main results,

Lemma 2.1.

The following two dissections hold:

(2.1)
(2.2)

Hirschhorn, Garvan and Borwein [14] have proved Eqn (2.1). For proof of (2.2), see [15].

Lemma 2.2.

The following two dissections hold:

(2.3)
(2.4)

Eqn (2.3) was proved by Baruah and Ojah [16]. Replacing q by − q in (2.3) and using the fact that (q;q)=f23f1f4, we get (2.4).

Lemma 2.3.

The following two dissections hold:

(2.5)
(2.6)

Xia and Yao [17] gave a proof of Lemma (2.3). Replacing q by − q in (2.5) and using the fact that (q;q)=f23f1f4, we get (2.6).

Lemma 2.4.

The following two dissections hold:

(2.7)
(2.8)

Xia and Yao [18] proved (2.7) by employing an addition formula for theta functions.

Lemma 2.5.

The following two dissections hold:

(2.9)

Eqn (2.9) was proved by Hirschhorn and Sellers [19].

Lemma 2.6.

The following three dissections hold:

(2.10)

One can see this identity in [20].

Lemma 2.7.

(Cui and Gu [21, Theorem 2.2]). For any prime p ≥ 5,

where
Lemma 2.8.

For any prime p and positive integer n,

(2.11)

Setting i = 2, j = 4, δ = 8 and k = 3 in (1.8), we see that

(3.1)

By the definition of f(a, b) and the well-known Jacobi triple product identity, we get

(3.2)

Substituting (2.7) into (3.2), we have

(3.3)

Equating odd parts of the aforementioned equation, we obtain

(3.4)

Involving (2.11) in (3.4), we get

(3.5)

Employing (2.2) into (3.5), we arrive at

(3.6)

Extracting the terms involving q2n from both sides of (3.6), we have

(3.7)

Using (2.11) in the aforementioned equation, we obtain

(3.8)

Substituting (2.1) into (3.8), we find that

(3.9)

which implies

(3.10)

Invoking (2.11) in (3.10), the equation reduces to

(3.11)

Employing (2.8) into (3.11), we obtain

(3.12)

Congruence (1.9) easily follows from the aforementioned equation.

From (3.6), we have

(3.13)

Using (2.11) in (3.6), we found

(3.14)

Substituting (2.5) into (3.14), we obtain

(3.15)

Extracting the terms involving q2n+1 from (3.15), dividing by q and replacing q2 by q, we arrive at

(3.16)

Invoking (2.11) in (3.16), we get

(3.17)

Employing (2.1) into (3.17), we obtain

(3.18)

Extracting the terms involving q2n from both sides of (3.18), we have

(3.19)

Using (2.11) in (3.19), we arrive at

(3.20)

Congruence (1.11) easily follows from (3.20).

From (3.18), we have

(3.21)

Congruence (1.12) follows by extracting the terms involving q2n+1 from (3.21).

From (3.15), we get

(3.22)

Using (2.11) in (3.22), we obtain

(3.23)

Employing (2.1) into (3.23), we reduce that

(3.24)

Extracting the terms involving q2n from both sides of (3.24), we find that

(3.25)

Substituting (2.5) into (3.25), we arrive at

(3.26)

which implies

(3.27)

Invoking (2.11) in (3.27), we obtain

(3.28)

Congruence (1.13) follows by extracting the terms involving q2n+1 from (3.28).

Extracting the terms involving q2n+1 from (3.26), dividing by q and replacing q2 by q, we arrive at

(3.29)

Using (2.11) in (3.29), we get

(3.30)

Congruence (1.14) follows from (3.30).

Extracting the terms involving q2n from both sides of (3.24), we have

(3.31)

Employing (2.6) into (3.31), we found

(3.32)

which implies

(3.33)

Substituting (2.4) into (3.33), we get

(3.34)

which implies

(3.35)

Using (2.11) in (3.35), we find that

(3.36)

Employing (2.6) into (3.36), we get

(3.37)

Extracting the terms involving q2n from (3.37) and replacing q2 by q, we obtain

(3.38)

Invoking (2.11) in (3.38), we arrive at

(3.39)

Congruence (1.15) follows by extracting the terms involving q2n+1 from (3.39).

From (3.37), we have

(3.40)

Invoking (2.11) in (3.40), we obtain

(3.41)

Congruence (1.16) follows from (3.41).

From (3.34), we arrive at

(3.42)

Using (2.11) in (3.42), we get

(3.43)

From the equations (3.14) and (3.43), we obtain (1.17).

Extracting the terms involving q2n+1 from (3.9), dividing by q and replacing q2 by q, we obtain

(3.44)

Invoking (2.11) in (3.44), we get

(3.45)

Congruence (1.10) follows by extracting the terms involving q2n+1 from (3.45).

From equations (3.45), (3.30) and (3.40), we obtain (1.18).

Extracting the terms involving q2n from (3.45) and replacing q2 by q, we have

(4.1)

define

(4.2)

Combining (4.1) and (4.2), we find that

(4.3)

For a prime, p ≥ 5 or (p1)2k,mp12, consider

(4.4)

therefore,

Since 6p=1 the congruence relation (4.4) holds if and only if both k=m=±p16. Therefore, if we substitute Lemma (2.7) into (4.2) and then extract the terms in which the powers of q are congruent to 7p2724 modulo p and then divide by q7p2724, we find that

which implies that

(4.5)

and for n ≥ 0,

(4.6)

where i is an integer and 1 ≤ i ≤ p − 1. By induction, we see that for n ≥ 0 and α ≥ 0,

(4.7)

Replacing n by p2αn+7p2α724 in (4.3), we arrive at (1.19).

Replacing n by p2n+pi+7p2724 in (4.7) and using (4.6), we find that for n ≥ 0 and α ≥ 0,

(5.1)

Comparing coefficients of qn from both sides of (4.3), we see that for n ≥ 0,

(5.2)

The required result follows from (5.1) and (5.2).

Setting i = 2, j = 4, δ = 8 and k = 5 in (1.8), we see that

(6.1)

By the definition of f(a, b) and the well-known Jacobi triple product identity, we get

(6.2)

Substituting (2.9) into (6.2), we have

(6.3)

Equating odd parts of the aforementioned equation, we obtain

(6.4)

Involving (2.11) in (6.4), we get

(6.5)

Congruences (1.21) and (1.22) follow from the aforementioned equation.

From (6.5), we have

(7.1)

Employing Lemma (2.7) into (7.1), it can be see that

(7.2)

which implies

(7.3)

Therefore,

Using the aforementioned relation and by induction on α, we arrive at (1.23).

Combining (7.2) with Theorem (1.5), we derive that for α ≥ 0,

Therefore, it follows that

where l = 1, 2, …, p − 1, we obtain (1.24).

Setting i = 2, j = 4, δ = 12 and k = 3 in (1.8), we see that

(9.1)

By the definition of f(a, b) and the well-known Jacobi triple product identity, we get

(9.2)

Substituting (2.7) into (9.2), we have

(9.3)

Equating odd parts of the aforementioned equation, we obtain

(9.4)

Involving (2.11) in (9.4), we get

(9.5)

Ramanujan recorded the following identity in his third note book:

(9.6)

Substituting (9.6) into (9.5), we deduce that

(9.7)

Congruence (1.25) easily follows from the aforementioned equation.

Extracting the terms involving q3n+1 from (9.7), dividing by q and replacing q3 by q, we arrive at

(9.8)

Using (2.11) in (9.8), we get

(9.9)

Congruence (1.26) follows by extracting the terms involving q2n+1 from (9.9).

From (9.9), we can reduce that

(9.10)

Employing (2.10) into (9.10), we get

(9.11)

Congruence (1.27) follows from (9.11).

Extracting the terms involving q3n+1 from (9.11), dividing by q and replacing q3 by q, we have

(9.12)

Congruences (1.28) and (1.29) follow by extracting the terms involving q3n+1 and q3n+2 from (9.9).

From (9.12), we find that

(9.13)

Combining (9.10) and (9.13), we get

(9.14)

Using the aforementioned relation and by induction on α, we have

(9.15)

Using (1.28) in (9.15), we obtain (1.30).

From (9.11), we find that

(10.1)

Invoking (2.11) in (10.1), we obtain

(10.2)

Employing Lemma (2.7) into (10.2), it can be see that

(10.3)

which implies

(10.4)

Therefore,

Using the aforementioned relation and by induction on α, we arrive at (1.31).

Combining (10.3) with Theorem (1.8), we derive that for α ≥ 0,

Therefore, it follows that

where l = 1, 2, …, p − 1, we obtain (1.32).

Dedicated to Prof. M. S. Mahadeva Naika on his 62nd birthday.

The authors would like to thank the anonymous referee for his valuable suggestions to improve the quality of our paper.

Funding: This research received no specific grants from any funding agency in the public, commercial or not for profit sectors.

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