OFFSET
0,5
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..450
FORMULA
a(n) mod 2 = 1.
a(n) mod 10 = period 5: repeat [1,1,1,1,7], g.f.: (7*x^4+x^3+x^2+x+1)/(1-x^5).
EXAMPLE
a(4) = 7: (1)(2)(3)(4), (1234), (1243), (1324), (1342), (1423), (1432).
MAPLE
a:= proc(n) option remember; `if`(n=0, 1, add(`if`(isprime(j), 0,
a(n-j)*binomial(n-1, j-1)*(j-1)!), j=1..n))
end:
seq(a(n), n=0..25);
MATHEMATICA
a[n_] := a[n] = If[n == 0, 1, Sum[If[PrimeQ[j], 0,
a[n-j] Binomial[n-1, j-1] (j-1)!], {j, 1, n}]];
Table[a[n], {n, 0, 25}] (* Jean-François Alcover, Oct 31 2021, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 24 2019
STATUS
approved