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 A100256 #12 Aug 21 2025 03:00:22 %S A100256 0,4,49,225,676,1600,3249,5929,10000,15876,24025,34969,49284,67600, %T A100256 90601,119025,153664,195364,245025,303601,372100,451584,543169,648025, %U A100256 767376,902500,1054729,1225449,1416100,1628176,1863225,2122849 %N A100256 Squares of second pentagonal numbers: a(n) = (1/4)*n^2*(3*n+1)^2. %H A100256 Leonhard Euler, <a href="http://math.dartmouth.edu/~euler/pages/E542.html">De mirabilibus proprietatibus numerorum pentagonalium</a>, par. 29 %H A100256 Leonhard Euler, <a href="https://arxiv.org/abs/math/0505373">On the remarkable properties of the pentagonal numbers</a>, arXiv:math/0505373 [math.HO], 2006. %F A100256 G.f.: x*(4+29*x+20*x^2+x^3)/(1-x)^5. - _Colin Barker_, Feb 14 2012 %Y A100256 Equals A005449(n)^2. Cf. A100255. %K A100256 nonn,easy %O A100256 0,2 %A A100256 _Ralf Stephan_, Nov 13 2004