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 A371778 #8 Apr 06 2024 10:04:27
%S A371778 1,5,28,166,1015,6324,39901,254035,1628380,10493680,67914088,
%T A371778 441086947,2873255906,18763759019,122803467241,805241108334,
%U A371778 5288922607095,34789875710568,229147231044397,1511104857207706,9975701630282920,65920216186587257
%N A371778 a(n) = Sum_{k=0..floor(n/3)} binomial(3*n+2,n-3*k).
%F A371778 a(n) = [x^n] 1/(((1-x)^3-x^3) * (1-x)^(2*n)).
%o A371778 (PARI) a(n) = sum(k=0, n\3, binomial(3*n+2, n-3*k));
%Y A371778 Cf. A371777, A371779, A371780.
%Y A371778 Cf. A066380.
%K A371778 nonn
%O A371778 0,2
%A A371778 _Seiichi Manyama_, Apr 05 2024