OFFSET
0,13
COMMENTS
a(n) is also the excess of the number of labeled factorizations of n over the number of ordered factorizations (see the Munagi link for definition of labeled factorization)
LINKS
Antti Karttunen, Table of n, a(n) for n = 0..10000 (computed from the b-files of A074206 and A104725)
A. O. Munagi, Labeled factorization of integers, Electron. J. Combin. 16 (2009), no. 1, Research Paper 50, 17pp.
FORMULA
a(n) = Sum(ordfac(n,k)*(Bell(k-1)-1),k=1..Omega(n)), where ordfac(n,k)=number of ordered factorizations of n into k factors.
EXAMPLE
MAPLE
a:=proc(n::integer) local u, r, i, j, k; if n<2 then return 0; end if; u:=map(x->x[2], ifactors(n)[2]); r:=add(u[i], i=1..nops(u)); add(add((-1)^i*binomial(k, i)*product(binomial(u[j]+k-i-1, u[j]), j=1..nops(u)), i=0..k-1)*(bell(k-1)-1), k=1..r); end proc: seq(a(n), n=0..99);
CROSSREFS
KEYWORD
nonn
AUTHOR
Augustine O. Munagi, May 01 2009
STATUS
approved