OFFSET
1,9
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
FORMULA
MATHEMATICA
Table[Length[Select[Divisors[n], OddQ[#]&&!PrimeQ[#]&]], {n, 80}] (* Harvey P. Dale, May 06 2012 *)
a[n_] := DivisorSigma[0, n/2^IntegerExponent[n, 2]] - PrimeNu[n] + If[OddQ[n], 0, 1]; Array[a, 100] (* Amiram Eldar, Jul 01 2022 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d%2) && !isprime(d)); \\ Michel Marcus, May 05 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved