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 A026580 #8 Oct 19 2021 21:59:49 %S A026580 1,2,5,12,30,75,189,478,1211,3076,7818,19901,50680,129179,329383, %T A026580 840336,2144540,5474889,13980493,35709394,91228015,233108456, %U A026580 595740568,1522725379,3892624055,9952119054,25446913766,65072487645 %N A026580 T(n,0) + T(n,1) + ... + T(n,n), T given by A026568. %F A026580 Conjecture: n*a(n) +(n-2)*a(n-1) +(-17*n+28)*a(n-2) +5*(-n+4)*a(n-3) +2*(34*n-107)*a(n-4) +16*(n-5)*a(n-5) +32*(-2*n+9)*a(n-6)=0. - _R. J. Mathar_, Jun 23 2013 %Y A026580 Cf. A026568. %K A026580 nonn %O A026580 0,2 %A A026580 _Clark Kimberling_