A369005 - OEIS

%I #14 Jun 02 2024 14:39:13

%S 1,12,15,28,35,39,44,51,55,76,81,87,91,92,95,111,115,119,123,124,143,

%T 144,155,159,172,180,183,187,188,189,203,215,219,225,235,236,247,256,

%U 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

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

%C This is a multiplicative semigroup; if m and n are in the sequence then so is m*n. - _Antti Karttunen_, Jun 02 2024

%H Antti Karttunen, <a href="/A369005/b369005.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) \\ See A369004

%Y Positions of multiples of 4 in A083345.

%Y Setwise difference A369002 \ A373265.

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

%Y Cf. A369004 (characteristic function).

%Y Cf. A373259 (subsequence).

%Y Cf. also A369644, A369007.

%K nonn

%O 1,2

%A _Antti Karttunen_, Jan 14 2024