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 A071896 #18 Jan 13 2025 04:06:56
%S A071896 1,4,25,254,3835,80789,2265927,81654161,3676703172,202300328621,
%T A071896 13355498392158,1041931174916945,94829092415834153,
%U A071896 9958096634837503010,1195066425272916195353,162538991933751440071018,24869660832289243247061107
%N A071896 CONTINUANT transform of triangular numbers 1, 3, 6, 10, ...
%C A071896 Equals the eigensequence of an infinite lower triangular matrix with (1, 3, 6, ...) in the main diagonal and (1, 1, 1, ...) in the subdiagonal; with the rest zeros. - _Gary W. Adamson_, Apr 13 2009
%H A071896 Alois P. Heinz, <a href="/A071896/b071896.txt">Table of n, a(n) for n = 1..200</a>
%H A071896 N. J. A. Sloane, <a href="/transforms.txt">Transforms</a>
%p A071896 a:= proc(n) option remember; `if`(n<0, 0,
%p A071896 `if`(n=0, 1, n*(n+1)/2 *a(n-1) +a(n-2)))
%p A071896 end:
%p A071896 seq(a(n), n=1..20); # _Alois P. Heinz_, Aug 06 2013
%t A071896 a[n_] := a[n] = If[n < 0, 0, If[n == 0, 1, n*(n+1)/2*a[n-1] + a[n-2]]];
%t A071896 Table[a[n], {n, 1, 20}] (* _Jean-François Alcover_, Jan 13 2025, after _Alois P. Heinz_ *)
%K A071896 nonn
%O A071896 1,2
%A A071896 _N. J. A. Sloane_, Jun 10 2002