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a(0) = 1; a(n) = 6 * Sum_{k=1..n} binomial(n,k) * a(k-1).
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%I #5 Jun 07 2021 14:55:37

%S 1,6,48,414,3876,38946,416808,4722774,56379756,706236426,9250945008,

%T 126342991614,1794459834036,26445918969906,403610795535288,

%U 6367606516836774,103683034842399996,1739933892930544986,30052751213767045248,533635421576480845134,9730601644306627161156

%N a(0) = 1; a(n) = 6 * Sum_{k=1..n} binomial(n,k) * a(k-1).

%F G.f. A(x) satisfies: A(x) = 1 + 6 * x * A(x/(1 - x)) / (1 - x)^2.

%t a[0] = 1; a[n_] := a[n] = 6 Sum[Binomial[n, k] a[k - 1], {k, 1, n}]; Table[a[n], {n, 0, 20}]

%t nmax = 20; A[_] = 0; Do[A[x_] = 1 + 6 x A[x/(1 - x)]/(1 - x)^2 + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]

%Y Cf. A040027, A094419, A144223, A343523, A343975, A344735, A344840, A345078, A345081.

%K nonn

%O 0,2

%A _Ilya Gutkovskiy_, Jun 07 2021