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 A370781 #13 Aug 18 2025 05:45:01
%S A370781 1,1,4,10,37,121,442,1576,5818,21466,80272,301324,1138762,4320226,
%T A370781 16459132,62904664,241134553,926678569,3569385772,13776307714,
%U A370781 53267766997,206304355225,800203300354,3108008802064,12086612436376,47056902019336,183400211694496
%N A370781 Expansion of 1 / ( (1 - x)*(1 + 2*x)*(1 - 4*x) )^(1/3).
%F A370781 a(n) ~ 2^(2*n+1) / (Gamma(1/3) * 3^(2/3) * n^(2/3)). - _Vaclav Kotesovec_, Mar 10 2024
%F A370781 a(n) = Sum_{k=0..floor(n/2)} A004987(k) * binomial(n,2*k). - _Seiichi Manyama_, Aug 18 2025
%o A370781 (PARI) my(N=30, x='x+O('x^N)); Vec(1/((1-x)*(1+2*x)*(1-4*x))^(1/3))
%o A370781 (PARI) a(n) = sum(k=0, n\2, (-9)^k*binomial(-1/3, k)*binomial(n, 2*k)); \\ _Seiichi Manyama_, Aug 18 2025
%Y A370781 Cf. A004987, A370145.
%K A370781 nonn
%O A370781 0,3
%A A370781 _Seiichi Manyama_, Mar 01 2024