A347202 - OEIS

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

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OFFSET

1,2

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

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 *)

PROG

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

CROSSREFS

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

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

Sequence in context: A048300 A178953 A182653 * A036349 A352827 A364290

Adjacent sequences: A347199 A347200 A347201 * A347203 A347204 A347205

KEYWORD

nonn

AUTHOR

Omar E. Pol, Aug 22 2021

STATUS

approved