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arXiv 0905.0635math.NTmath.CO
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关于多边形数的泛和

On universal sums of polygonal numbers

Zhi-Wei Sun

摘要:

对于$m=3,4,\ldots$,$m$阶的多边形数由$p_m(n)=(m-2)\binom n2+n\ (n=0,1,2,\ldots)$给出。对于正整数$a,b,c$和具有$\max\{i,j,k\}\ge5$的$i,j,k\ge3$,我们称三元组$(ap_i,bp_j,cp_k)$是泛的,如果对于任何$n=0,1,2,\ldots$都存在非负整数$x,y,z$使得$n=ap_i(x)+bp_j(y)+cp_k(z)$。我们发现,只有95个候选人的通用三元组(其中两个是$(p_4,p_5,p_6)$和$(p_3,p_4,p_{27})$),并推测,他们确实是通用三元组。对于许多三元组$(ap_i,bp_j,cp_k)$(包括$(p_3,4p_4,p_5),(p_4,p_5,p_6)$和$(p_4,p_4,p_5)$),我们证明了任何非负整数都可以写成$ap_i(x)+bp_j(y)+cp_k(z)$ with $x,y,z\in\mathbb Z$的形式.我们也给出了一些有关三元二次型的新结果,其中之一是任何非负整数$n\equiv 1\pmod{6}$都可以写成$x^2+3y^2+24z^2$ with $x,y,z\in\mathbb Z$的形式。此外,我们提出了几个相关的结构,其中之一的状态,任何$m=3,4,\ldots$的每个自然数可以表示为$p_{m+1}(x_1)+p_{m+2}(x_2)+p_{m+3}(x_3)+r$与$x_1,x_2,x_3\in\{0,1,2,\ldots\}$和$r\in\{0,\ldots,m-3\}$。

英文摘要:

For $m=3,4,\ldots$, the polygonal numbers of order $m$ are given by $p_m(n)=(m-2)\binom n2+n\ (n=0,1,2,\ldots)$. For positive integers $a,b,c$ and $i,j,k\ge3$ with $\max\{i,j,k\}\ge5$, we call the triple $(ap_i,bp_j,cp_k)$ universal if for any $n=0,1,2,\ldots$ there are nonnegative integers $x,y,z$ such that $n=ap_i(x)+bp_j(y)+cp_k(z)$. We show that there are only 95 candidates for universal triples (two of which are $(p_4,p_5,p_6)$ and $(p_3,p_4,p_{27})$), and conjecture that they are indeed universal triples. For many triples $(ap_i,bp_j,cp_k)$ (including $(p_3,4p_4,p_5),(p_4,p_5,p_6)$ and $(p_4,p_4,p_5)$), we prove that any nonnegative integer can be written in the form $ap_i(x)+bp_j(y)+cp_k(z)$ with $x,y,z\in\mathbb Z$. We also show some related new results on ternary quadratic forms, one of which states that any nonnegative integer $n\equiv 1\pmod{6}$ can be written in the form $x^2+3y^2+24z^2$ with $x,y,z\in\mathbb Z$. In addition, we pose several related conjectures one of which states that for any $m=3,4,\ldots$ each natural number can be expressed as $p_{m+1}(x_1)+p_{m+2}(x_2)+p_{m+3}(x_3)+r$ with $x_1,x_2,x_3\in\{0,1,2,\ldots\}$ and $r\in\{0,\ldots,m-3\}$.

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