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 A090428 #15 Feb 16 2025 08:32:51 %S A090428 1,6,9,10,12,15,16,21,28,36,45,55,64,66,70,81,91,105,120,145,153,171, %T A090428 176,190,196,210,225,231,276,280,325,378,400,435,441,477,496,540,561, %U A090428 595,616,630,651,703,715,780,833,861,936,946,1035,1089,1105,1128,1216 %N A090428 Numbers that are k-gons for two or more k's, where k = 3, 4, 5, ..., 16. %H A090428 Amiram Eldar, <a href="/A090428/b090428.txt">Table of n, a(n) for n = 1..10000</a> %H A090428 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PolygonalNumber.html">Polygonal Number</a>. %o A090428 (PARI) is(n,c=2)=for(s=3,16, ispolygonal(n,s)&&!c--&&return(s)) \\ _M. F. Hasler_, Jan 19 2017 %Y A090428 Cf. A062712, A090466. %K A090428 nonn %O A090428 1,2 %A A090428 _Eric W. Weisstein_, Nov 30 2003