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 A370272 #7 Feb 14 2024 10:48:36
%S A370272 1,1,3,13,51,201,819,3382,14067,58927,248303,1051128,4466787,19043766,
%T A370272 81418746,348936288,1498601459,6448162221,27791057997,119954739879,
%U A370272 518451715551,2243481128020,9718784202240,42143960004750,182917942802595,794589638379576
%N A370272 Coefficient of x^n in the expansion of 1/( (1-x) * (1-x^3) )^n.
%F A370272 a(n) = Sum_{k=0..floor(n/3)} binomial(n+k-1,k) * binomial(2*n-3*k-1,n-3*k).
%F A370272 The g.f. exp( Sum_{k>=1} a(k) * x^k/k ) has integer coefficients and equals (1/x) * Series_Reversion( x * (1-x) * (1-x^3) ).
%o A370272 (PARI) a(n, s=3, t=1, u=1) = sum(k=0, n\s, binomial(t*n+k-1, k)*binomial((u+1)*n-s*k-1, n-s*k));
%Y A370272 Cf. A063030.
%K A370272 nonn
%O A370272 0,3
%A A370272 _Seiichi Manyama_, Feb 13 2024