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 A105018 #18 Feb 16 2025 08:32:57
%S A105018 12,17,19,26,27,32,35,37,51,55,56,58,61,62,63,64,69,71,75,77,79,80,82,
%T A105018 84,89,90,91,94,99,100,101,102,106,107,108,111,112,113,114,115,118,
%U A105018 119,120,122,123,124,125,129,133,134,135,137,139,140,141,142,144,146,151
%N A105018 Indices of the irregular primes.
%D A105018 Carl Ludwig Siegel, Zu zwei Bemerkungen Kummers, Nachrichten der Akademie der Wissenschaften in Göttingen, 1964, pp. 51-57.
%H A105018 Amiram Eldar, <a href="/A105018/b105018.txt">Table of n, a(n) for n = 1..10000</a>
%H A105018 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/IrregularPrime.html">Irregular Prime</a>.
%F A105018 Conjecture (Siegel, 1964): Limit_{n -> oo} a(n)/n = 1 - 1 / sqrt(e) (A290506). Of the 788060 primes < 12000000, 310443 are irregular.
%F A105018 A000040(a(n)) = A000928(n). - _Amiram Eldar_, Mar 06 2019
%t A105018 fQ[n_] := Block[{ p = Prime[ n ], k = 1}, While[ 2k <= p - 3 && Mod[ Numerator[ BernoulliB[ 2k]], p] != 0, k++ ]; If[ 2k != p - 1, True, False]]; Select[ Range[2, 151], fQ[ # ] &]
%Y A105018 Cf. A000040, A000928, A105019, A290506.
%K A105018 nonn
%O A105018 1,1
%A A105018 _Robert G. Wilson v_, Mar 31 2005