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 A381818 #13 Mar 08 2025 09:40:20
%S A381818 1,2,12,97,903,9129,97419,1080058,12319200,143630575,1704099034,
%T A381818 20507897766,249734145622,3071587654688,38102046141882,
%U A381818 476138815310364,5988435287060671,75745116484532586,962898676577135634,12295850972794555196,157649023155654522723,2028662477759375282902
%N A381818 Expansion of ( (1/x) * Series_Reversion( x * ((1-x) / C(x))^2 ) )^(1/2), where C(x) is the g.f. of A000108.
%F A381818 G.f. A(x) satisfies A(x) = C(x*A(x)^2) / (1 - x*A(x)^2).
%F A381818 a(n) = Sum_{k=0..n} binomial(2*n+2*k+1,k) * binomial(3*n-k,n-k)/(2*n+2*k+1).
%o A381818 (PARI) my(N=30, x='x+O('x^N)); Vec((serreverse(x*((1-x)*2*x/(1-sqrt(1-4*x)))^2)/x)^(1/2))
%Y A381818 Cf. A381817, A381819, A381820.
%Y A381818 Cf. A364592, A381830, A381831.
%Y A381818 Cf. A000108, A381772.
%K A381818 nonn
%O A381818 0,2
%A A381818 _Seiichi Manyama_, Mar 07 2025