{Overleaf 模板库}LaTeX 模板 — Recent

So publish to gallery creates a template starting point for new documents? Aha. There's a check box at the bottom, "Let people use this project as a template."

Your abstract. \(\sum_{k=1}^{\ell}\sum_{j=0}^m A_{m,j}k^j(T-k)^j=\sum_{k=0}^{m}(-1)^{m-k}U_m(\ell,k)\cdot T^k=T^{2m+1}, \ \ell=T\in\mathbb{N}.\)