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 A379281 #10 Dec 20 2024 02:42:04
%S A379281 1,4,18,96,575,3706,25078,175666,1262723,9261018,69024147,521281642,
%T A379281 3980391050,30678331440,238350850248,1864751821958,14678131286357,
%U A379281 116160233811868,923684828888152,7376541052964806,59137050311947284,475757909357776656,3839678158239147611
%N A379281 G.f. A(x) satisfies A(x) = 1/( (1 - x) * (1 - x*A(x)) )^2.
%F A379281 G.f.: B(x)^2 where B(x) is the g.f. of A199475.
%F A379281 a(n) = 2 * Sum_{k=0..n} binomial(2*n-k+2,k) * binomial(3*n-3*k+1,n-k)/(2*n-k+2).
%o A379281 (PARI) a(n) = 2*sum(k=0, n, binomial(2*n-k+2, k)*binomial(3*n-3*k+1, n-k)/(2*n-k+2));
%Y A379281 Cf. A379282, A379283.
%Y A379281 Cf. A199475.
%K A379281 nonn
%O A379281 0,2
%A A379281 _Seiichi Manyama_, Dec 19 2024