OFFSET
0,4
COMMENTS
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..444
FORMULA
E.g.f.: sinh(x)*exp(x^2/(1-x)). More generally, e.g.f. for number of partitions of {1, 2, ...n} into lists with an odd number of lists of size k is sinh(x^k)*exp(x/(1-x)-x^k).
E.g.f.: sinh(x)*exp(x^2/(1-x))=1/2*Q(0); Q(k)=1-((2x-1)^k)/( 1-x/(x-((2x-1)^k)*(k+1)*(1-x)/Q(k+1))); (continued fraction). - Sergei N. Gladkovskii, Nov 17 2011
a(n) ~ (exp(1)-exp(-1)) * 2^(-3/2) * exp(2*sqrt(n)-n-3/2) * n^(n-1/4) * (1 + (43/48 - coth(1))/sqrt(n)). - Vaclav Kotesovec, Dec 01 2021
MAPLE
b:= proc(n, t) option remember; `if`(n=0, t, add(b(n-j,
`if`(j=1, 1-t, t))*binomial(n-1, j-1)*j!, j=1..n))
end:
a:= n-> b(n, 0):
seq(a(n), n=0..30); # Alois P. Heinz, May 10 2016
MATHEMATICA
b[n_, t_] := b[n, t] = If[n==0, t, Sum[b[n-j, If[j==1, 1-t, t]]*Binomial[ n-1, j-1]*j!, {j, 1, n}]]; a[n_] := b[n, 0]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Feb 03 2017, after Alois P. Heinz *)
PROG
(Python)
from sympy.core.cache import cacheit
from sympy import binomial, factorial as f
@cacheit
def b(n, t): return t if n==0 else sum([b(n - j, (1 - t if j==1 else t))*binomial(n - 1, j - 1)*f(j) for j in range(1, n + 1)])
def a(n): return b(n, 0)
print([a(n) for n in range(51)]) # Indranil Ghosh, Aug 10 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Vladeta Jovovic, Nov 19 2005; corrected Jun 06 2006
EXTENSIONS
More terms from David Wasserman, Feb 11 2009
a(0)=0 prepended by Alois P. Heinz, May 10 2016
STATUS
approved