This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A369005 #14 Jun 02 2024 14:39:13 %S A369005 1,12,15,28,35,39,44,51,55,76,81,87,91,92,95,111,115,119,123,124,143, %T A369005 144,155,159,172,180,183,187,188,189,203,215,219,225,235,236,247,256, %U A369005 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 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). %C A369005 This is a multiplicative semigroup; if m and n are in the sequence then so is m*n. - _Antti Karttunen_, Jun 02 2024 %H A369005 Antti Karttunen, <a href="/A369005/b369005.txt">Table of n, a(n) for n = 1..10000</a> %o A369005 (PARI) \\ See A369004 %Y A369005 Positions of multiples of 4 in A083345. %Y A369005 Setwise difference A369002 \ A373265. %Y A369005 Subsequence of A368995, which is a subsequence of A327864, which is a subsequence of A235992. %Y A369005 Cf. A369004 (characteristic function). %Y A369005 Cf. A373259 (subsequence). %Y A369005 Cf. also A369644, A369007. %K A369005 nonn %O A369005 1,2 %A A369005 _Antti Karttunen_, Jan 14 2024