OFFSET
1,2
FORMULA
a(n) = T(n,4), T(n,k) = Sum_{j=1..n} Stirling1(n,j) * T(j,k-1), k>1, T(n,1) = (n-1)!.
MATHEMATICA
T[n_, 1] := (n - 1)!; T[n_, k_] := T[n, k] = Sum[StirlingS1[n, j] * T[j, k - 1], {j, 1, n}]; a[n_] := T[n, 4]; Array[a, 20] (* Amiram Eldar, Feb 11 2022 *)
PROG
(PARI) my(N=40, x='x+O('x^N)); Vec(serlaplace(-log(1-log(1+log(1+log(1+x))))))
(PARI) T(n, k) = if(k==1, (n-1)!, sum(j=1, n, stirling(n, j, 1)*T(j, k-1)));
a(n) = T(n, 4);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Feb 11 2022
STATUS
approved