OFFSET
0,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..440
FORMULA
From Gary W. Adamson, Jul 14 2011: (Start)
Let M = triangle A128175 as an infinite square production matrix (deleting the first "1"):
1, 1, 0, 0, 0, ...
2, 2, 1, 0, 0, ...
4, 4, 3, 1, 0, ...
8, 8, 7, 4, 1, ...
...
a(n) = sum of top row terms of M^(n-1). Example: top row of M^4 = (71, 71, 38, 10, 1), sum = 191 = a(5). (End)
a(0) = 1, a(n) = n * a(n-1) + Sum_{j=1..n} A003319(j) * a(n - j), with offset 0 for the term 1. - F. Chapoton, Feb 26 2018
MATHEMATICA
T[n_, k_]:= T[n, k]= If[n<k || k<0, 0, If[n==k, 1, If[n==k+1, n, k*T[n, k+1] + Sum[T[j, 0]*T[n, j+k+1], {j, 0, n-k-1}]]]];
a[n_]:= T[n, 1];
Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Aug 09 2018 *)
PROG
(PARI) {a(n) = if(n<0, 0, (matrix(n+2, n+2, m, j, if(m==j, 1, if(m==j+1, -m+1, -polcoeff((1-1/sum(i=0, m, i!*x^i))/x +O(x^m), m-j-1))))^-1)[n+1, 2])}
(Sage)
@CachedFunction
def T(n, k):
if (k<0 or k>n): return 0
elif (k==n): return 1
elif (k==n-1): return n
else: return k*T(n, k+1) + sum( T(j, 0)*T(n, j+k+1) for j in (0..n-k-1) )
[T(n, 1) for n in (0..30)] # G. C. Greubel, Jun 07 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Apr 10 2005
STATUS
approved