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 A370274 #8 Feb 14 2024 10:48:28
%S A370274 1,1,3,16,67,276,1212,5391,24003,107719,486728,2208735,10059868,
%T A370274 45970367,210657177,967636566,4454109123,20540731356,94882599285,
%U A370274 438931979661,2033217678792,9429562243530,43779688919145,203463271733010,946445226206940,4406251540834026
%N A370274 Coefficient of x^n in the expansion of 1/( (1-x) * (1-x^3)^2 )^n.
%F A370274 a(n) = Sum_{k=0..floor(n/3)} binomial(2*n+k-1,k) * binomial(2*n-3*k-1,n-3*k).
%F A370274 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)^2 ). See A369296.
%o A370274 (PARI) a(n, s=3, t=2, u=1) = sum(k=0, n\s, binomial(t*n+k-1, k)*binomial((u+1)*n-s*k-1, n-s*k));
%Y A370274 Cf. A369296.
%K A370274 nonn
%O A370274 0,3
%A A370274 _Seiichi Manyama_, Feb 13 2024