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 A307904 #13 May 05 2019 16:00:59
%S A307904 1,1,1,10,49,151,901,5881,28225,165565,1158601,6993196,44201521,
%T A307904 320103070,2200745821,15118248601,113390231809,845797019077,
%U A307904 6250243032145,48718551529210,384815404148401,3021055319338813,24492293678972725,202303201125303565,1669594463059152961
%N A307904 Coefficient of x^n in (1 + x + n*x^3)^n.
%F A307904 a(n) = Sum_{k=0..floor(n/3)} n^k * binomial(n,3*k) * binomial(3*k,k).
%F A307904 log(a(n)) ~ (n/3 - 1/2)*log(n) + (log(3) - 2*log(2)/3)*n + (2*n)^(2/3)/3 - (2*n)^(1/3)/9. - _Vaclav Kotesovec_, May 05 2019
%t A307904 Table[HypergeometricPFQ[{1/3 - n/3, 2/3 - n/3, -n/3}, {1/2, 1}, -27*n/4], {n, 0, 25}] (* _Vaclav Kotesovec_, May 05 2019 *)
%o A307904 (PARI) {a(n) = polcoef((1+x+n*x^3)^n, n)}
%o A307904 (PARI) {a(n) = sum(k=0, n\3, n^k*binomial(n, 3*k)*binomial(3*k, k))}
%Y A307904 Cf. A116411, A187018, A307903, A307905.
%K A307904 nonn
%O A307904 0,4
%A A307904 _Seiichi Manyama_, May 05 2019