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 A339880 #27 Jan 07 2021 10:41:27 %S A339880 15,51,85,91,255,435,451,561,595,771,1105,1261,1285,1351,1695,2091, %T A339880 2431,2465,3655,3855,4369,4795,5083,5151,5383,6601,6643,6735,7051, %U A339880 8245,8481,8695,8911,8995,9061,9605,10585,11155,13107,15051,15211,16405,16705,17733,18721,19669,20451,21845,22359,23001,26335,28645 %N A339880 Odd composite numbers k such that A053575(k) [the odd part of phi] divides k-1. %C A339880 No common terms with A016105. See A339870 for the reason. - _Antti Karttunen_, Dec 26 2020 %H A339880 Antti Karttunen, <a href="/A339880/b339880.txt">Table of n, a(n) for n = 1..1237</a> %o A339880 (PARI) %o A339880 A000265(n) = (n>>valuation(n, 2)); %o A339880 isA339880(n) = (bitand(n,1)&&(n>1)&&!isprime(n)&&!((n-1)%A000265(eulerphi(n)))); %Y A339880 Cf. A000010, A000265, A016105, A053575. %Y A339880 Subsequence of A005117 and of A339879, and of A340077. %Y A339880 Cf. A339869, A339870 (subsequences). %Y A339880 Cf. also A002997, A053576, A339817. %K A339880 nonn %O A339880 1,1 %A A339880 _Antti Karttunen_, Dec 24 2020