This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A027252 #9 Oct 26 2019 16:16:44
%S A027252 1,3,10,28,80,211,569,1455,3806,9564,24565,61080,155041,382920,964163,
%T A027252 2370712,5934974,14548685,36266755,88711181,220415107,538305745,
%U A027252 1334040167,3254193849,8047710361,19613210297,48419611161
%N A027252 a(n) = Sum_{k=0..n} (k+1) * A026780(n, n-k).
%K A027252 nonn
%O A027252 0,2
%A A027252 _Clark Kimberling_