Even universal sums of triangular numbers

Jangwon Ju

For an arbitrary integer $x$, an integer of the form $T(x)=\frac{x^2+x}{2}$ is called a triangular number. Let ${\alpha }_1,\dots ,{\alpha }_k$ be positive integers. A sum $Δ_{α_1,\dots,α_k}(x_…