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 A117263 #6 Jun 06 2020 21:31:03
%S A117263 1,2,7,64,1729,140050,34032151,24809438080,54258241080961,
%T A117263 355988319732185122,7006918097288599756327,
%U A117263 413751506726794527011353024,73294838162131470076480154142529
%N A117263 Row sums of triangle A117262; also, self-convolution of A117264.
%F A117263 a(n) = Sum_{k=0..n} 3^( n*(n-1)/2 - k*(k-1)/2 ).
%F A117263 G.f. A(x) satisfies: A(x) = 1/(1 - x) + x * A(3*x). - _Ilya Gutkovskiy_, Jun 06 2020
%o A117263 (PARI) a(n)=sum(k=0,n,3^((n-k)*(n+k-1)/2))
%Y A117263 Cf. A117261, A117262, A117264.
%K A117263 nonn
%O A117263 0,2
%A A117263 _Paul D. Hanna_, Mar 14 2006