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 Recently, Elsholtz showed that k=12 in an unpublished manuscript.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 N2≫N1>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 N2≫N1>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=N1/9−2ϵi,Qi=N8/9+ϵi,L=log2N1 |
for i=1,2.
For any integers a1,a2,q1,q2 satisfying
1⩽a1⩽q1⩽P1,(a1,q1)=1, |
1⩽a2⩽q2⩽P2,(a2,q2)=1, |
we can define the major arcs M1, M2 and minor arcs m1, m2 as usual, namely
Mi=⋃q⩽Pi⋃1⩽a⩽q(a,q)=1Mi(a,q),mi=[1/Qi,1+1/Qi]∖Mi, |
where i=1,2 and
Mi(a,q)={αi∈[0,1]:|αi−a/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:α1∈M1,α2∈M2}, |
m=[1/Qi,1+1/Qi]2∖M. |
As in [3], for convenience, let d=10−4 and
Ui=(Ni16(1+d))1/3,Vi=U5/6i |
for i=1,2. Let
S(αi,Ui)=∑p∼Ui(logp)e(p3αi),T(αi,Vi)=∑p∼Vi(logp)e(p3αi), |
G(αi)=∑v⩽Le(2vαi), |
Eλ={αi∈[0,1]:|G(αi)|⩾λL}, |
where i=1,2.
Let
r(N1,N2)=∑logp1logp2⋯logp16 |
denote the weighted number of solutions of (1.3) in (p1,...,p16,v1,...,vk) with
p1,...,p4∼U1,p5,...,p8∼V1, |
p9,...,p12∼U2,p13,...p16∼V2,vj⩽L, |
where j=1,2,...,k. Then we have
r(N1,N2)=(∬M+∬m⋂Eλ+∬m∖Eλ)S4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)×Gk(α1+α2)e(−α1N1−α2N2)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 N2≫N1>N2.
For a Dirichlet character χ mod q, let
C(χ,a)=q∑h=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)=q∑a=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 N1≡N2≡0(mod 2), A(Ni,k)={ni⩾2:ni=Ni−2v1−⋯−2vk} and k⩾35. Then we have
∑n1∈A(N1,k)n2∈A(N2,k)n1≡n2≡0(mod 2)S(n1)S(n2)⩾0.89094Lk. |
Proof. For k⩾35,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(1−128)∏p>3(1+A(ni,p)), |
∏p⩾17(1+A(n,p))⩾C0:=0.82067. |
Let m0=14. Now we can get
∑n1∈B(N1,k)n2∈B(N2,k)n1≡n2≡0(mod 2)S(n1)S(n2)⩾(1.9921875C0)2∑n1∈B(N1,k)n2∈B(N2,k)n1≡n2≡0(mod 2)∏3<p<m0(1+A(n1,p))∏3<p<m0(1+A(n2,p))⩾(1.9921875C0)2∑1⩽j⩽q∑n1∈B(N1,k)n2∈B(N2,k)n1≡n2≡0(mod 2)n1≡n2≡j(mod q)∏3<p<m0(1+A(n1,p))∏3<p<m0(1+A(n2,p))⩾(1.9921875C0)2∑1⩽j⩽q∏3<p<m0(1+A(j,p))∏3<p<m0(1+A(j,p))∑n1∈B(N1,k)n2∈B(N2,k)n1≡n2≡0(mod 2)n1≡n2≡j(mod q)1,⩾(1.9921875C0)2∑1⩽j⩽q∏3<p<m0(1+A(j,p))2∑n1∈B(N1,k)n1≡0(mod 2)n1≡j(mod q)1, |
where q=∏3<p<m0p. By the result obtained by Zhao and Ge [16,Lemma 2.3], we have
∑n1∈B(N1,k)n1≡0(mod 2)n1≡j(mod q)1⩾(1−0.000064)Lk3q+O(Lk−1). |
Noting that
p∑j=1(1+A(j,p))2=p+2p∑j=1A(j,p)+p∑j=1(A(j,p))2=p+p∑j=1(A(j,p))2⩾p, |
therefore
∑n1∈B(N1,k)n2∈B(N2,k)n1≡n2≡0(mod 2)S(n1)S(n2)⩾(1.9921875C0)2p∑j=1∏3<p<m0(1+A(j,p))2(1−0.000064)Lk3q+O(Lk−1)⩾13(1.9921875C0)2∏3<p<m0p∑j=1(1+A(j,p))2(1−0.000064)Lkq+O(Lk−1)⩾13(1.9921875C0)2(1−0.000064)Lk+O(Lk−1). |
Then the lemma follows since L is sufficiently large.
Lemma 2.2. Let N1 and N2 are sufficiently large positive even integers satisfying N2≫N1>N2,
r1(N1,N2)⩾1.26×10−4U1V41U2V42Lk. |
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(−α1N1−α2N2)dα1dα2⩾(138)2∑n1∈A(N1,k)n2∈A(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 1⩽a⩽q,(a,q)=1 and |λ|⩽1/qQ, with Q=U12/7; then, we have
∑p∼U(logp)e(p3α)≪U1−1/12+ϵ+q−1/6U1+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,
maxα∈C(M)|S(αi,Ui)|≪U1−1/12+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)≪N−E(λ)1, |
with E(0.9532)>8/9+10−10.
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 N2≫N1>N2,
r2(N1,N2)≪U1V41U2V42Lk−1, |
with λ=0.9532.
Proof. According to the definition of m, we have
m⊂{(α1,α2):α1∈m1,α2∈[0,1]}∪{(α1,α2):α1∈[0,1],α2∈m2}. |
Then
r2(N1,N2)=∬m⋂EλS4(α1,U1)T4(α1,V1)S4(α2,U2)T4(α2,V2)×Gk(α1+α2)e(−α1N1−α2N2)dα1dα2≪Lk(∬(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)|dα1dα2≪U11/3+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)|dα2≪U2V42. |
From Lemma 2.5 we have
∬(α1,α2)∈[0,1]2|G(α1+α2)|⩾λL|S4(α2,U2)T4(α2,V2)|dα1dα2≪U2V42N−E(λ)1. |
We choose λ=0.9532 and get
I1≪U11/3−8/3−ϵ1V41U2V42≪U1−ϵ1V41U2V42, |
since N2≫N1>N2. Similarly,
I2≪U11/3−8/3−ϵ2V42U1V41≪U1−ϵ2V42U1V41, |
Then
r2(N1,N2)≪(U1−ϵ1V41U2V42+U1−ϵ2V42U1V41)Lk≪U1V41U2V42Lk−1. |
To estimate r3(N1,N2), first we need to consider the upper bound for the number of solutions of the equation
n=p31+⋯+p34−p35−⋯−p38,0⩽|n|⩽Ni. | (2.1) |
Lemma 2.7. Let n≡0(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,p6∼Ui,p3,p4,p7,p8∼Vi,i=1,2. |
Then for all 0⩽|n|⩽Ni,
ϱi(n)⩽bUiV4iL−8 |
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 N2≫N1>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)k∫10|S4(α1,U1)T4(α1,V1)|dα1∫10|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)>1.26×10−4U1V41U2V42Lk−117.04λkU1V41U2V42Lk. |
Therefore we solve the inequality
r(N1,N2)>0 |
and obtain k⩾287. 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 N2≫N1>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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