A369005 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

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

PROG

(PARI) \\ See A369004

CROSSREFS

Positions of multiples of 4 in A083345.

Setwise difference A369002 \ A373265.