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 A360663 #12 Feb 16 2025 08:34:04
%S A360663 3,4,5,6,7,8,3,10,11,4,13,14,5,16,17,3,19,20,7,22,23,4,25,26,9,28,29,
%T A360663 3,31,32,11,34,35,6,37,38,13,4,41,7,43,44,3,46,47,8,49,5,17,52,53,9,
%U A360663 55,56,19,58,59,4,61,62,3,64,65,11,67,68,23,7,71,12,73,74,5,76,77,13,79
%N A360663 a(n) is the least integer m >= 3 such that n is a centered m-gonal number.
%H A360663 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CenteredPolygonalNumber.html">Centered Polygonal Number</a>.
%H A360663 Wikipedia, <a href="https://en.wikipedia.org/wiki/Centered_polygonal_number">Centered polygonal number</a>.
%e A360663 a(16) = 5 since 16 is a centered pentagonal number, but not a centered square or centered triangular number.
%t A360663 seq[len_] := Module[{s = Table[0, {len}], c = 0, k = 3, n, ckn}, While[c < len, n = 2; While[(ckn = k*n*(n - 1)/2 - 2) <= len, If[s[[ckn]] == 0, c++; s[[ckn]] = k]; n++]; n = 4; k++]; s]; seq[100] (* _Amiram Eldar_, Mar 06 2023 *)
%Y A360663 Cf. A101321, A176774, A333914.
%K A360663 nonn
%O A360663 4,1
%A A360663 _Ilya Gutkovskiy_, Feb 15 2023