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 A187122 #8 May 10 2025 23:15:04
%S A187122 1,9,81,855,10758,159633,2750067,54178485,1204443432,29871630837,
%T A187122 818490738402,24571782872034,802459134168208,28332664539686670,
%U A187122 1075700621922471621,43710289920461797346,1893011243289589171122
%N A187122 A diagonal of triangle A187120.
%C A187122 Definition of triangle: A187120(n,k) = [y^k] R_{n-1}(y+y^2) for k=3..n, n>3, where R_n(y) is the n-th row polynomial starting with R_3(y)=y^3.
%F A187122 Equals column 2 in the matrix cube of triangle A135080.
%o A187122 (PARI) {a(n)=local(Rn=y^3);for(m=3,n+1,Rn=subst(truncate(Rn),y,y+y^2+O(y^m)));polcoeff(Rn,n,y)}
%Y A187122 Cf. A187120, A135083, A187121, A187123, A187124.
%K A187122 nonn
%O A187122 3,2
%A A187122 _Paul D. Hanna_, Mar 08 2011