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 A091031 #8 Aug 30 2025 02:43:41 %S A091031 1,16,114,644,3270,15642,72072,323752,1428102,6214520,26761196, %T A091031 114287736,484816540,2045277990,8588492100,35923392720,149753379270, %U A091031 622458753840,2580709189740,10675646755800,44074384410420,181638630107220,747375951913344,3070765657798704 %N A091031 Third to last entries in rows of array A090452 (scaled (3,2)-Stirling2). %F A091031 a(n) = A090452(n, 2*(n-1)), n>=2. %F A091031 a(n) = (9*n^2-19*n+8)*(n-1)*C(n)/(4*(2*n-1)), n>=2; with the Catalan numbers C(n) = A000108(n). %F A091031 a(n) ~ 9 * 2^(2*n-3) * sqrt(n/Pi). - _Amiram Eldar_, Aug 30 2025 %t A091031 a[n_] := (9*n^2 - 19*n + 8)*(n-1) * CatalanNumber[n]/(4*(2*n-1)); Array[a, 25, 2] (* _Amiram Eldar_, Aug 30 2025 *) %Y A091031 Cf. A000108 (last row entries), 3*A002054(n-1) (second to last row entries), A000108, A090452. %K A091031 nonn,easy,changed %O A091031 2,2 %A A091031 _Wolfdieter Lang_, Jan 09 2004