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 A166259 #16 Feb 16 2025 08:33:11 %S A166259 2,18,32,50,72,98,128,162,200,242,338,392,450,512,578,648,722,882,968, %T A166259 1058,1152,1250,1352,1458,1682,1800,1922,2048,2178,2312,2401,2450, %U A166259 2662,2738,2809,2888,3042,3174,3200,3362,3528,3698,3750,4050,4225,4232,4418,4489,4608,4802 %N A166259 Positive integers n such that a centered polygonal number n*k*(k+1)/2+1 is not a square for any k > 0. %C A166259 Positive integers n such that A120744(n) = -1. %H A166259 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CenteredPolygonalNumber.html">Centered Polygonal Number</a>. %Y A166259 Cf. A120744, A001542, A006451, A001921, A129444, A001570, A001652, A129556, A053606, A105038, A105040, A053141, A061278. %K A166259 nonn %O A166259 1,1 %A A166259 _Alexander Adamchuk_, Oct 10 2009 %E A166259 Edited and extended by _Max Alekseyev_, Jan 20 2010