A329609 Numbers k such that A156552(k) is a multiple of 3.

1, 4, 9, 10, 16, 21, 22, 25, 30, 34, 36, 39, 40, 46, 49, 55, 57, 62, 64, 66, 81, 82, 84, 85, 87, 88, 90, 91, 94, 100, 102, 105, 111, 115, 118, 120, 121, 129, 133, 134, 136, 138, 144, 146, 154, 155, 156, 159, 160, 166, 169, 183, 184, 186, 187, 189, 194, 195, 196, 198, 203, 205, 206, 213, 218, 220, 225, 228, 235, 237, 238, 246

Offset: 1

Author

Antti Karttunen, Nov 21 2019

Keywords

• nonn

Comments

Not a multiplicative semigroup. For example, although 10 and 21 are present, 210 is missing. Compare to A332820. - Antti Karttunen, Jan 17 2023

Links

• Antti Karttunen, Table of n, a(n) for n = 1..20000

Crossrefs

Cf. A000290 (subsequence), A156552, A329603, A329604, A332812.

Positions of zeros in A329903, of nonzeros in A341353, of ones in A353269 (characteristic function), A353418 (Dirichlet inverse of char.fun), A359836.

Sequence A332449 sorted into ascending order.

Cf. also A353303, A353304 and A332820.

Programs

PARI

A156552(n) = {my(f = factor(n), p2 = 1, res = 0); for(i = 1, #f~, p = 1 << (primepi(f[i, 1]) - 1); res += (p * p2 * (2^(f[i, 2]) - 1)); p2 <<= f[i, 2]); res}; \\ From A156552
isA329609(n) = !(A156552(n)%3);