OFFSET
1,4
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..16384
Antti Karttunen, Data supplement: n, a(n) computed for n = 1..100000
FORMULA
Dirichlet g.f.: 1/Product_{n > 1}(1 - A045778(n)/n^s).
EXAMPLE
The a(24) = 16 twice-factorizations:
(2)*(2)*(2)*(3),
(2)*(2)*(2*3), (2)*(2)*(6), (2)*(3)*(4),
(2)*(2*6), (2)*(3*4), (2)*(12), (3)*(2*4), (3)*(8), (4)*(2*3), (4)*(6),
(2*3*4), (2*12), (3*8), (4*6), (24).
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
Table[Sum[Times@@(Length[Select[facs[#], UnsameQ@@#&]]&/@fac), {fac, facs[n]}], {n, 100}]
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 05 2017
STATUS
approved