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 A216911 #24 Feb 16 2025 08:33:18 %S A216911 3,11,17,5,47,89,101,197,29,263,521,1559,173,3011,71,641,1277,53,317, %T A216911 4583,617,4019,401,3041,41,479,3347,131,10427,4643,1301,419,6689,5531, %U A216911 281,55217,251,2417,4001,491,1601,3137,449,3617,107,2969,4211,6737,1061 %N A216911 Numbers that are a prime factor of a Carmichael number divisible by 3, listed in the order in which they appear in the prime factorizations of such Carmichael numbers. %C A216911 Every term, other than a(1)=3, is a prime of the form 6*k - 1. %H A216911 Charles R Greathouse IV, <a href="/A216911/b216911.txt">Table of n, a(n) for n = 1..3744</a> %H A216911 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CarmichaelNumber.html">Carmichael Number</a> %e A216911 The first few Carmichael numbers that are divisible by 3 (A258801), their prime factorizations, and the terms of this sequence are as follows: %e A216911 . %e A216911 m | A258801(m) & prime factorization | prime factors not appearing earlier %e A216911 --+----------------------------------+---------------------------------------- %e A216911 1 | 561 = 3 * 11 * 17 | a(1) = 3, a(2) = 11, a(3) = 17; %e A216911 2 | 62745 = 3 * 5 * 47 * 89 | a(4) = 5, a(5) = 47, a(6) = 89; %e A216911 3 | 656601 = 3 * 11 * 101 * 197 | a(7) = 101, a(8) = 197; ... %Y A216911 Cf. A002997 (Carmichael numbers), A258801 (Carmichael numbers divisible by 3). %K A216911 nonn %O A216911 1,1 %A A216911 _Marius Coman_, Sep 20 2012 %E A216911 a(26), a(34), a(43) corrected by _Charles R Greathouse IV_, Sep 20 2012