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 A081918 #6 Jun 02 2025 00:15:48 %S A081918 1,1,5,36,352,4375,66096,1176490,24117248,559607373,14500000000, %T A081918 414998793616,13002646487040,442663617327139,16271152851709952, %U A081918 642244372558593750,27093655358260903936,1216529796891671712025 %N A081918 a(0) = 1; a(n) = n^(n-1)(3n-1)/2 (n>0). %C A081918 Main diagonal of square array T(n,k) where T(n,k)=k^n(n^2-n+2k^2)/(2k^2), in which rows have g.f. (1-2kx+(k^2+1)x^2)/(1-kx)^3. %H A081918 Vincenzo Librandi, <a href="/A081918/b081918.txt">Table of n, a(n) for n = 0..101</a> %F A081918 a(0)=1, a(n)=a(n)=n^n(n^2-n+2n^2)/(2n^2), n>0. %Y A081918 Cf. A000124, A081908, A081909, A081910, A081911, A081912. %K A081918 easy,nonn %O A081918 0,3 %A A081918 _Paul Barry_, Mar 31 2003