A033272 Number of odd nonprimes dividing n.

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

G. C. Greubel, Table of n, a(n) for n = 1..1000

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

Adjacent sequences: A033269 A033270 A033271 * A033273 A033274 A033275

Keyword

nonn

Author

N. J. A. Sloane

Status

approved