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E.g.f. satisfies A(x) = exp(x^3*A(x)^2) / (1-x).
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%I #12 Feb 16 2025 08:34:06

%S 1,1,2,12,96,840,9720,143640,2399040,45239040,976752000,23537606400,

%T 621444700800,17936155036800,562855739846400,19038932398886400,

%U 690456599575142400,26748823900403404800,1102407824344284057600,48147134965603914240000

%N E.g.f. satisfies A(x) = exp(x^3*A(x)^2) / (1-x).

%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LambertW-Function.html">Lambert W-Function</a>.

%F E.g.f.: sqrt(LambertW( -2*x^3/(1-x)^2 ) / (-2*x^3)).

%F a(n) = n! * Sum_{k=0..floor(n/3)} (2*k+1)^(k-1) * binomial(n-k,n-3*k)/k!.

%o (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(sqrt(lambertw(-2*x^3/(1-x)^2)/(-2*x^3))))

%o (PARI) a(n) = n!*sum(k=0, n\3, (2*k+1)^(k-1)*binomial(n-k, n-3*k)/k!);

%Y Cf. A360601, A370875.

%K nonn,changed

%O 0,3

%A _Seiichi Manyama_, Mar 09 2024