A369005 Numbers k for which k' / gcd(k,k') is a multiple of four, where k' stands for the arithmetic derivative of k, A003415(k).

1, 12, 15, 28, 35, 39, 44, 51, 55, 76, 81, 87, 91, 92, 95, 111, 115, 119, 123, 124, 143, 144, 155, 159, 172, 180, 183, 187, 188, 189, 203, 215, 219, 225, 235, 236, 247, 256, 259, 267, 268, 284, 287, 291, 295, 297, 299, 303, 316, 319, 320, 323, 327, 332, 335, 336, 339, 355, 371, 391, 395, 400, 403, 407, 411, 412, 415

Offset: 1

Author

Antti Karttunen, Jan 14 2024

Keywords

• nonn

Comments

This is a multiplicative semigroup; if m and n are in the sequence then so is m*n. - Antti Karttunen, Jun 02 2024

Links

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

Crossrefs

Positions of multiples of 4 in A083345.

Setwise difference A369002 \ A373265.

Subsequence of A368995, which is a subsequence of A327864, which is a subsequence of A235992.

Cf. A369004 (characteristic function).

Cf. A373259 (subsequence).

Cf. also A369644, A369007.

Programs

PARI

\\ See A369004