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 A371785 #7 Apr 06 2024 10:03:46
%S A371785 1,3,14,76,441,2652,16303,101727,641630,4080154,26112384,167978615,
%T A371785 1085182436,7035477777,45750406205,298279844724,1949096816505,
%U A371785 12761551428024,83701819019155,549850618355886,3617119500327536,23824816811652905,157106267803712709
%N A371785 a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(3*n-k,n-2*k).
%F A371785 a(n) = [x^n] 1/((1-x+x^2) * (1-x)^(2*n)).
%o A371785 (PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(3*n-k, n-2*k));
%Y A371785 Cf. A024718, A371786, A371787.
%Y A371785 Cf. A371742.
%K A371785 nonn
%O A371785 0,2
%A A371785 _Seiichi Manyama_, Apr 06 2024