OFFSET
0,4
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..220
FORMULA
E.g.f.: Product_{k>0} cosh(x^(2*k-1)/(2*k-1)).
EXAMPLE
a(2)=1 because we have (1)(2)(3)(4).
MAPLE
g:=product(cosh(x^(2*k-1)/(2*k-1)), k=1..40): gser:=series(g, x=0, 35): seq(factorial(2*n)*coeff(gser, x, 2*n), n=0..14); # Emeric Deutsch, Aug 25 2007
# second Maple program:
with(combinat):
b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0, add(
`if`(j=0 or irem(i, 2)=1 and irem(j, 2)=0, multinomial(n,
n-i*j, i$j)*(i-1)!^j/j!*b(n-i*j, i-1), 0), j=0..n/i)))
end:
a:= n-> b(2*n$2):
seq(a(n), n=0..20); # Alois P. Heinz, Mar 09 2015
MATHEMATICA
multinomial[n_, k_] := n!/Times @@ (k!); b[n_, i_] := b[n, i] = If[n == 0, 1, If[i<1, 0, Sum[If[j == 0 || Mod[i, 2] == 1 && Mod[j, 2] == 0, multinomial[n, Join[{n-i*j}, Array[i&, j]]]*(i-1)!^j/j!*b[n-i*j, i-1], 0], {j, 0, n/i}]]]; a[n_] := b[2n, 2n]; Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Feb 08 2017, after Alois P. Heinz *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Vladeta Jovovic, Aug 11 2007
EXTENSIONS
More terms from Emeric Deutsch, Aug 25 2007
STATUS
approved