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A033272
Number of odd nonprimes dividing n.
2
1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 1, 2, 1, 1, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 1, 1, 4, 1, 1, 1, 2, 2, 2, 1, 1, 3, 2, 1, 2, 1, 1, 2, 1, 1, 4, 1, 2, 2, 1, 1, 2, 2, 1, 2, 1, 1, 4, 1, 2, 2, 1, 1
OFFSET
1,9
LINKS
FORMULA
a(n) = A001227(n) - A005087(n). - Amiram Eldar, Jul 01 2022
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
Cf. A001227 (with odd divisors), A005087, A033273 (with nonprime divisors).
Sequence in context: A257990 A369257 A257743 * A324907 A331295 A325133
KEYWORD
nonn
STATUS
approved