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 A187007 #13 Feb 01 2025 14:57:44
%S A187007 1,3,12,69,538,5404,67092,997581,17337444,345547750,7778860028,
%T A187007 195365725310,5418540898800,164556820433116,5432639292242576,
%U A187007 193765826638479112,7426524928340527902,304439910637309354106,13293321078232321952036,616016966059346344408690,30196821383142448481822800
%N A187007 A diagonal of triangle A187005.
%C A187007 Definition of triangle: A187005(n,k) = [y^k] R_{n-1}(y+y^2) for k=1..n where R_n(y) is the n-th row polynomial for n>1 with R_1(y)=y.
%o A187007 (PARI) {a(n)=local(Rn=y);for(m=1,n+2,Rn=subst(truncate(Rn),y,y+y^2+y*O(y^m)));polcoeff(Rn,n,y)}
%Y A187007 Cf. A187005, A135081, A187006, A187008, A187009.
%K A187007 nonn
%O A187007 1,2
%A A187007 _Paul D. Hanna_, Mar 02 2011
%E A187007 More terms from _Michel Marcus_, Feb 01 2025