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Research article

On pairs of equations in eight prime cubes and powers of 2

  • Received: 23 September 2022 Revised: 17 November 2022 Accepted: 23 November 2022 Published: 30 November 2022
  • MSC : 11P32, 11P05, 11P55

  • In this paper, it is proved that every pair of large positive even integers satisfying some necessary conditions can be represented in the form of a pair of eight cubes of primes and 287 powers of 2. This improves the previous result.

    Citation: Gen Li, Liqun Hu, Xianjiu Huang. On pairs of equations in eight prime cubes and powers of 2[J]. AIMS Mathematics, 2023, 8(2): 3940-3948. doi: 10.3934/math.2023197

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  • In this paper, it is proved that every pair of large positive even integers satisfying some necessary conditions can be represented in the form of a pair of eight cubes of primes and 287 powers of 2. This improves the previous result.



    In 1951 and 1953, Linnik [4,5] considered a problem related to Goldbach's problem. He proved that each sufficiently large positive even integer N can be written as a sum of two primes and k powers of 2, namely

    N=p1+p2+2ν1++2νk. (1.1)

    Later in 2002, Heath-Brown and Puchta [1] showed that k=13 and k=7 under the assumption of Generalized Riemann Hypothesis. In 2003, Pintz and Ruzsa [12] obtained that k=8 unconditionally. Recently, Elsholtz showed that k=12 in an unpublished manuscript. This was also proved by Liu and Lü [11] independently.

    In 2001, Liu and Liu [6] showed that each large positive even integer N was a sum of eight prime cubes and k powers of 2, namely

    N=p31+p32++p38+2v1++2vk. (1.2)

    The acceptable value was improved by Liu and Lü [8], Platt and Trudgian [13] and Zhao and Ge [16].

    As an extension, recently, Liu [10] considered that every pair of large positive even integers satisfying N2N1>N2 can be written as

    {N1=p31+p32++p38+2v1++2vk,N2=p39+p310++p316+2v1++2vk. (1.3)

    He proved that (1.3) was solvable when k=1432. Later Platt and Trudgian [13], Zhao [15] and Liu [7] improved it to 1319,648 and 609, respectively.

    In this paper, we sharpened the above result and obtained the following theorem.

    Theorem 1.1. For k=287, the concurrent equations of (1.3) are solvable for every pair of sufficiently large positive even integers N1 and N2 satisfying N2N1>N2.

    We can establish Theorem 1.1 by using the Hardy-Littlewood circle method in combination with some new technologies of Hu et al. [2] and Hu and Yang [3].

    Now we can give an outline for the proof of Theorem 1.1.

    Let Ni with i=1,2 be sufficiently large positive even integers. As in [8], in order to use the circle method, we set

    Pi=N1/92ϵi,Qi=N8/9+ϵi,L=log2N1

    for i=1,2.

    For any integers a1,a2,q1,q2 satisfying

    1a1q1P1,(a1,q1)=1,
    1a2q2P2,(a2,q2)=1,

    we can define the major arcs M1, M2 and minor arcs m1, m2 as usual, namely

    Mi=qPi1aq(a,q)=1Mi(a,q),mi=[1/Qi,1+1/Qi]Mi,

    where i=1,2 and

    Mi(a,q)={αi[0,1]:|αia/q|1/(qQi)}.

    By the definitions of Pi and Qi, we know that the arcs Mi(a,q) are disjoint. We also let

    M=M1×M2={(α1,α2)[0,1]2:α1M1,α2M2},
    m=[1/Qi,1+1/Qi]2M.

    As in [3], for convenience, let d=104 and

    Ui=(Ni16(1+d))1/3,Vi=U5/6i

    for i=1,2. Let

    S(αi,Ui)=pUi(logp)e(p3αi),T(αi,Vi)=pVi(logp)e(p3αi),
    G(αi)=vLe(2vαi),
    Eλ={αi[0,1]:|G(αi)|λL},

    where i=1,2.

    Let

    r(N1,N2)=logp1logp2logp16

    denote the weighted number of solutions of (1.3) in (p1,...,p16,v1,...,vk) with

    p1,...,p4U1,p5,...,p8V1,
    p9,...,p12U2,p13,...p16V2,vjL,

    where j=1,2,...,k. Then we have

    r(N1,N2)=(M+mEλ+mEλ)S4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)×Gk(α1+α2)e(α1N1α2N2)dα1dα2:=r1(N1,N2)+r2(N1,N2)+r3(N1,N2).

    We can prove Theorem 1.1 by estimating r1(N1,N2), r2(N1,N2) and r3(N1,N2). We want to show that r(N1,N2)>0 for N2N1>N2.

    For a Dirichlet character χ mod q, let

    C(χ,a)=qh=1¯χ(h)e(ah3q),C(q,a)=C(χ0,a).

    If χ1,...,χ8 are characters mod q, then we write

    B(n,q;χ1,...,χ8)=qa=1(a,q)=1C(χ1,a)C(χ2,a)C(χ8,a)e(anq),
    B(n,q)=B(n,q;χ0,...,χ0),
    A(n,q)=B(n,q)φ4(q),S(n)=q=1A(n,q).

    Lemma 2.1. Let N1N20(mod 2), A(Ni,k)={ni2:ni=Ni2v12vk} and k35. Then we have

    n1A(N1,k)n2A(N2,k)n1n20(mod 2)S(n1)S(n2)0.89094Lk.

    Proof. For k35,A(ni,pk)=0. Now since A(ni,p) is multiplicative, we can get

    S(ni)=p=2(1+A(ni,p)).

    With a similar argument of Lemma 2.3 in the paper by Zhao [15], we have

    S(ni)=2(1128)p>3(1+A(ni,p)),
    p17(1+A(n,p))C0:=0.82067.

    Let m0=14. Now we can get

    n1B(N1,k)n2B(N2,k)n1n20(mod 2)S(n1)S(n2)(1.9921875C0)2n1B(N1,k)n2B(N2,k)n1n20(mod 2)3<p<m0(1+A(n1,p))3<p<m0(1+A(n2,p))(1.9921875C0)21jqn1B(N1,k)n2B(N2,k)n1n20(mod 2)n1n2j(mod q)3<p<m0(1+A(n1,p))3<p<m0(1+A(n2,p))(1.9921875C0)21jq3<p<m0(1+A(j,p))3<p<m0(1+A(j,p))n1B(N1,k)n2B(N2,k)n1n20(mod 2)n1n2j(mod q)1,(1.9921875C0)21jq3<p<m0(1+A(j,p))2n1B(N1,k)n10(mod 2)n1j(mod q)1,

    where q=3<p<m0p. By the result obtained by Zhao and Ge [16,Lemma 2.3], we have

    n1B(N1,k)n10(mod 2)n1j(mod q)1(10.000064)Lk3q+O(Lk1).

    Noting that

    pj=1(1+A(j,p))2=p+2pj=1A(j,p)+pj=1(A(j,p))2=p+pj=1(A(j,p))2p,

    therefore

    n1B(N1,k)n2B(N2,k)n1n20(mod 2)S(n1)S(n2)(1.9921875C0)2pj=13<p<m0(1+A(j,p))2(10.000064)Lk3q+O(Lk1)13(1.9921875C0)23<p<m0pj=1(1+A(j,p))2(10.000064)Lkq+O(Lk1)13(1.9921875C0)2(10.000064)Lk+O(Lk1).

    Then the lemma follows since L is sufficiently large.

    Lemma 2.2. Let N1 and N2 are sufficiently large positive even integers satisfying N2N1>N2,

    r1(N1,N2)1.26×104U1V41U2V42Lk.

    Proof. By Lemma 2.1 in Liu and Lü [8], we note that

    r1(N1,N2)=MS4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)×Gk(α1+α2)e(α1N1α2N2)dα1dα2(138)2n1A(N1,k)n2A(N2,k)S(n1)S(n2)J(n1)J(n2).

    We also note that J(ni)>78.15468UiV4i by Liu and Lü [8,Lemma 3.3]. Then the lemma follows from Lemma 2.1.

    Lemma 2.3. Let α=a/q+λ be subject to 1aq,(a,q)=1 and |λ|1/qQ, with Q=U12/7; then, we have

    pU(logp)e(p3α)U11/12+ϵ+q1/6U1+ϵ(1+|λ|U3)1/2.

    Proof. This is Lemma 8.5 in Zhao [14].

    Lemma 2.4. Let m and S(αi,Ui) be defined as before; then,

    maxαC(M)|S(αi,Ui)|U11/12+ϵi.

    Proof. We can find that the proof of this lemma is similar to that of Lemma 3.4 in Liu and Lü [8]. We only need to change 1/14 to 1/12 for Lemma 2.4 in the proof of Liu and Lü [8,Lemma 3.4].

    Lemma 2.5. Let meas(Eλ) denotes the measure of Eλ. We have

    meas(Eλ)NE(λ)1,

    with E(0.9532)>8/9+1010.

    Proof. Similar to the proof of Liu and Lü [8,Lemma 3.5], we can calculate by computer to prove this lemma.

    Lemma 2.6. Let N1 and N2 are sufficiently large positive even integers satisfying N2N1>N2,

    r2(N1,N2)U1V41U2V42Lk1,

    with λ=0.9532.

    Proof. According to the definition of m, we have

    m{(α1,α2):α1m1,α2[0,1]}{(α1,α2):α1[0,1],α2m2}.

    Then

    r2(N1,N2)=mEλS4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)×Gk(α1+α2)e(α1N1α2N2)dα1dα2Lk((α1,α2)m1×[0,1]|G(α1+α2)|λL|S4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)|dα1dα2+(α1,α2)[0,1]×m2|G(α1+α2)|λL|S4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)|dα1dα2):=Lk(I1+I2).

    Then we have

    I1=(α1,α2)m1×[0,1]|G(α1+α2)|λL|S4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)|dα1dα2U11/3+ϵ1V41(α1,α2)[0,1]2|G(α1+α2)|λL|S4(α2,U2)T4(α2,V2)|dα1dα2,

    where we use Lemma 2.5 and the trivial bound of T(α1,V1).

    Now we use the variable substitution β=α1+α2 and get

    (α1,α2)[0,1]2|G(α1+α2)|λL|S4(α2,U2)T4(α2,V2)|dα1dα2=10|S4(α2,U2)T4(α2,V2)|(β[α2,1+α2]|G(β)|λLdβ)dα2.

    By Lemma 2.6 in the paper by Hu and Yang [3], we have

    10|S4(α2,U2)T4(α2,V2)|dα2U2V42.

    From Lemma 2.5 we have

    (α1,α2)[0,1]2|G(α1+α2)|λL|S4(α2,U2)T4(α2,V2)|dα1dα2U2V42NE(λ)1.

    We choose λ=0.9532 and get

    I1U11/38/3ϵ1V41U2V42U1ϵ1V41U2V42,

    since N2N1>N2. Similarly,

    I2U11/38/3ϵ2V42U1V41U1ϵ2V42U1V41,

    Then

    r2(N1,N2)(U1ϵ1V41U2V42+U1ϵ2V42U1V41)LkU1V41U2V42Lk1.

    To estimate r3(N1,N2), first we need to consider the upper bound for the number of solutions of the equation

    n=p31++p34p35p38,0|n|Ni. (2.1)

    Lemma 2.7. Let n0(mod 2) be an integer and ϱi(n) be the number of representations of n in the form of (2.1) that are subject to

    p1,p2,p5,p6Ui,p3,p4,p7,p8Vi,i=1,2.

    Then for all 0|n|Ni,

    ϱi(n)bUiV4iL8

    with b=147185.22.

    Proof. This lemma is Lemma 2.1 in the paper by Liu [9].

    Lemma 2.8. Let N1 and N2 be sufficiently large positive even integers satisfying N2N1>N2,

    r3(N1,N2)117.04λkU1V41U2V42Lk.

    Proof. According to the definitions of m and Eλ, by Lemma 2.7 and the definition of ϱ(n) we have

    r3(N1,N2)(λL)k(α1,α2)[0,1]2|S4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)|dα1dα2(λL)k10|S4(α1,U1)T4(α1,V1)|dα110|S4(α2,U2)T4(α2,V2)|dα2(λL)k(log(2U1))4(log(2V1))4(log(2U2))4(log(2V2))4ϱ1(0)ϱ2(0)117.04λkU1V41U2V42Lk.

    Combining Lemmas 2.2, 2.6 and 2.8, we can obtain

    r(N1,N2)>1.26×104U1V41U2V42Lk117.04λkU1V41U2V42Lk.

    Therefore we solve the inequality

    r(N1,N2)>0

    and obtain k287. Now the proof of Theorem 1.1 is complete.

    To sum up, we deduce that every pair of sufficiently large even integers N1, N2 satisfying N2N1>N2 can be represented in the form of a pair of eight cubes of primes and 287 powers of 2.

    This work was supported by the Natural Science Foundation of Jiangxi Province for Distinguished Young Scholars (Grant No. 20212ACB211007), Natural Science Foundation of China (Grant No. 11761048) and Natural Science Foundation of Tianjin City (Grant No. 19JCQNJC14200). The authors would like to express their sincere thanks to the referee for many useful suggestions and comments on the manuscript.

    The authors declare that they have no competing interests.



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