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 A381784 #7 Mar 07 2025 10:47:20
%S A381784 1,2,15,153,1799,22969,309479,4331175,62349575,917335467,13732751589,
%T A381784 208509835114,3203279694575,49701110565986,777708690091907,
%U A381784 12258870836704797,194475105262057575,3102607480658510165,49746656826517452788,801205735002960886531,12956005807148939155717
%N A381784 G.f. A(x) satisfies A(x) = (1 + x*A(x)^4) * C(x*A(x)^2), where C(x) is the g.f. of A000108.
%F A381784 a(n) = (1/(4*n+1)) * Sum_{k=0..n} binomial(4*n+1,k) * binomial(4*n-2*k+1,n-k).
%o A381784 (PARI) a(n) = sum(k=0, n, binomial(4*n+1, k)*binomial(4*n-2*k+1, n-k))/(4*n+1);
%Y A381784 Cf. A234461, A381774.
%Y A381784 Cf. A000108.
%K A381784 nonn
%O A381784 0,2
%A A381784 _Seiichi Manyama_, Mar 07 2025