A373587 Numbers k for which A373149(k) is odd, where A373149 is fully additive with a(2) = 1 and a(p) = prevprime(p) for odd primes p.

2, 5, 6, 7, 8, 11, 13, 15, 17, 18, 19, 20, 21, 23, 24, 28, 29, 31, 32, 33, 37, 39, 41, 43, 44, 45, 47, 50, 51, 52, 53, 54, 57, 59, 60, 61, 63, 67, 68, 69, 70, 71, 72, 73, 76, 79, 80, 83, 84, 87, 89, 92, 93, 96, 97, 98, 99, 101, 103, 107, 109, 110, 111, 112, 113, 116, 117, 123, 124, 125, 127, 128, 129, 130, 131, 132

Offset: 1

Author

Antti Karttunen, Jun 13 2024

Keywords

• nonn
• easy

Comments

Numbers such that the number of their prime factors (with multiplicity, A001222) and their 3-adic valuation (A007949) have different parity.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000

Crossrefs

Positions of odd terms in A373149, positions of 0's in A373585.

Cf. A001222, A007949, A373586 (complement).

Programs

Mathematica

Select[Range[200], OddQ[PrimeOmega[#] - IntegerExponent[#, 3]] &] (* Paolo Xausa, Dec 17 2024 *)

PARI

isA373587(n) = !A373585(n);

Formula

{k | A001222(k)+A007949(k) == 1 (mod 2)}.