Ternary universal sums of generalized polygonal numbers

Abstract

An integer of the form $p_m(x)=\frac{(m-2)x^2-(m-4)x}{2}(m\ge 3)$, for some integer $x$ is called a generalized polygonal number of order $m$. A ternary sum ${\Phi }_{i,j,k}^{a,b,c}(x,y,z)=a{p}_{i+2}(x)+b{p}_{j+2}(y)+c{p}_{k+2}(z)$ of generalized polygonal numbers, for some positive integers $a,b,c$ and some integers $1\le i\le j\le k$, is said to be universal over $\mathbb{Z}$ if the equation ${\Phi }_{i,j,k}^{a,b,c}(x,y,z)=n$ has an integer solution $x,y,z$ for any nonnegative integer $n$. In this article, we prove the universalities of $17$ ternary sums of generalized polygonal numbers, which was conjectured by Sun.

20 pages

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