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 A368893 #11 Jan 09 2024 08:45:55
%S A368893 1,1,4,30,288,3500,51876,908607,18374656,421492491,10815040000,
%T A368893 306944040931,9547373318400,322972830958648,11805432990665664,
%U A368893 463673398064821875,19474259980847153152,870954834559130974358,41323803842611198131264
%N A368893 a(n) = Sum_{k=0..floor(n/3)} n^(n-2*k) * binomial(n-2*k,k).
%F A368893 a(n) = [x^n] 1/(1 - n*x - n*x^3).
%F A368893 a(n) ~ n^n. - _Vaclav Kotesovec_, Jan 09 2024
%t A368893 Join[{1}, Table[n^n * HypergeometricPFQ[{1/3 - n/3, 2/3 - n/3, -n/3}, {1/2 - n/2, -n/2}, -27/(4*n^2)], {n, 1, 20}]] (* _Vaclav Kotesovec_, Jan 09 2024 *)
%o A368893 (PARI) a(n) = sum(k=0, n\3, n^(n-2*k)*binomial(n-2*k, k));
%Y A368893 Cf. A368891, A368892.
%Y A368893 Cf. A109516, A360727.
%K A368893 nonn,easy
%O A368893 0,3
%A A368893 _Seiichi Manyama_, Jan 09 2024