A331050 Positive integers whose number of factorizations into factors > 1 (A001055) is odd.

1, 2, 3, 5, 7, 8, 11, 13, 16, 17, 19, 23, 24, 27, 29, 30, 31, 32, 36, 37, 40, 41, 42, 43, 47, 53, 54, 56, 59, 60, 61, 64, 66, 67, 70, 71, 73, 78, 79, 81, 83, 84, 88, 89, 90, 96, 97, 100, 101, 102, 103, 104, 105, 107, 109, 110, 113, 114, 120, 125, 126, 127, 128

Offset

1,2

Comments

First differs from A319239 in lacking 256.

Links

Table of n, a(n) for n=1..63.

Mathematica

facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
Select[Range[100], OddQ[Length[facs[#]]]&]

Crossrefs

Complement of A331051.

The version for powers of two (instead of odds) is A330977.

The version for primes (instead of odds) is A330991.

Cf. A001055, A001221, A001222, A002033, A005117, A045778, A045782, A045783, A330972, A330973.

Sequence in context: A287893 A051600 A319239 * A026410 A066720 A079851

Adjacent sequences: A331047 A331048 A331049 * A331051 A331052 A331053

Keyword

nonn

Author

Gus Wiseman, Jan 10 2020

Status

approved