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 A176775 #8 Feb 16 2025 08:33:12
%S A176775 2,2,2,3,2,2,3,4,2,3,2,2,5,4,2,3,2,2,6,4,2,3,5,2,3,7,2,3,2,2,3,4,5,8,
%T A176775 2,2,3,4,2,3,2,2,9,4,2,3,7,2,6,4,2,3,10,2,3,4,2,3,2,2,3,8,5,11,2,2,3,
%U A176775 7,2,3,2,2,5,4,2,12,2,2,9,4,2,3,5,2,3,4,2,3,13,8,3,4,5,6,2,2,3,10,2,3,2,2
%N A176775 Index of n as m-gonal number for the smallest possible m (=A176774(n)).
%C A176775 a(n)=2 iff A176774(n)=n.
%H A176775 Michel Marcus, <a href="/A176775/b176775.txt">Table of n, a(n) for n = 3..10000</a>
%H A176775 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PolygonalNumber.html">Polygonal Number</a>.
%F A176775 a(n) = (m-4+sqrt((m-4)^2+8*(m-2)*n)) / (2*m-4), where m = A176774(n).
%o A176775 (PARI) f(n) = {k=3; while (! ispolygonal(n, k), k++); k; } \\ A176774
%o A176775 a(n) = my(m=f(n)); (m-4+sqrtint((m-4)^2+8*(m-2)*n)) / (2*m-4); \\ _Michel Marcus_, May 09 2021
%Y A176775 Cf. A176774.
%K A176775 nonn
%O A176775 3,1
%A A176775 _Max Alekseyev_, Apr 25 2010