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A213410
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G.f.: exp( Sum_{n>=1} binomial(3*n,n)^n/3^n * x^n/n ).
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1
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1, 1, 13, 7330, 185307558, 201002187396362, 9357300769149011773697, 18775362849239140086719414696830, 1631039199744298058694966065590003308698494, 6159916689356522044764167426829149420348399496664634288
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OFFSET
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0,3
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COMMENTS
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Compare to the g.f. G(x) = 1 + x*G(x)^3 of A001764: G(x) = exp( Sum_{n>=1} binomial(3*n,n)/3 * x^n/n ).
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LINKS
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FORMULA
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a(n) = (1/n) * Sum_{k=1..n} binomial(3*k,k)^k/3^k * a(n-k) for n>0 with a(0)=1.
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EXAMPLE
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G.f.: A(x) = 1 + x + 13*x^2 + 7330*x^3 + 185307558*x^4 + 201002187396362*x^5 +...
where
log(A(x)) = x + 5^2*x^2/2 + 28^3*x^3/3 + 165^4*x^4/4 + 1001^5*x^5/5 + 6188^6*x^6/6 + 38760^7*x^7/7 +...+ A025174(n)^n*x^n/n +...
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MATHEMATICA
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nmax = 10; b = ConstantArray[0, nmax+1]; b[[1]] = 1; Do[b[[n+1]] = 1/n*Sum[Binomial[3*k, k]^k/3^k * b[[n-k+1]], {k, 1, n}], {n, 1, nmax}]; b (* Vaclav Kotesovec, Mar 06 2014 *)
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PROG
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(PARI) {a(n)=polcoeff(exp(sum(m=1, n, binomial(3*m, m)^m/3^m*x^m/m)+x*O(x^n)), n)}
for(n=0, 15, print1(a(n), ", "))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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