A347202 Numbers whose number of odd divisors is not equal to 2.

1, 2, 4, 8, 9, 15, 16, 18, 21, 25, 27, 30, 32, 33, 35, 36, 39, 42, 45, 49, 50, 51, 54, 55, 57, 60, 63, 64, 65, 66, 69, 70, 72, 75, 77, 78, 81, 84, 85, 87, 90, 91, 93, 95, 98, 99, 100, 102, 105, 108, 110, 111, 114, 115, 117, 119, 120, 121, 123, 125, 126, 128, 129, 130

Offset: 1

Author

Omar E. Pol, Aug 22 2021

Keywords

• nonn

Comments

Numbers that are not products of an odd prime and a power of 2.

Numbers k such that the symmetric representation of sigma(k) has a number of subparts not equal to 2.

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Members of A266531 (sorted), except the column 2.

Cf. A001227, A038550 (complement), A237593, A279387 (subparts).

Programs

Maple

filter:= proc(n) not isprime(n/2^padic:-ordp(n,2)) end proc:
select(filter, [$1..200]); # Robert Israel, May 09 2025

Mathematica

A347202Q[k_] := !PrimeQ[k/2^IntegerExponent[k, 2]];
Select[Range[200], A347202Q] (* Paolo Xausa, May 12 2025 *)

PARI

isok(m) = sumdiv(m, d, d%2) != 2; \\ Michel Marcus, Aug 23 2021