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 A105018 Indices of the irregular primes. 2
 12, 17, 19, 26, 27, 32, 35, 37, 51, 55, 56, 58, 61, 62, 63, 64, 69, 71, 75, 77, 79, 80, 82, 84, 89, 90, 91, 94, 99, 100, 101, 102, 106, 107, 108, 111, 112, 113, 114, 115, 118, 119, 120, 122, 123, 124, 125, 129, 133, 134, 135, 137, 139, 140, 141, 142, 144, 146, 151 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Lim n -> Inf. a(n)/n = 1 -1 / sqrt(e). Of the 788060 primes < 12000000, 310443 are irregular. LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Irregular Prime. FORMULA A000040(a(n)) = A000928(n). - Amiram Eldar, Mar 06 2019 MATHEMATICA 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[ # ] &] CROSSREFS Cf. A000040, A000928, A105019. Sequence in context: A179243 A064825 A162918 * A154488 A302359 A214514 Adjacent sequences:  A105015 A105016 A105017 * A105019 A105020 A105021 KEYWORD nonn AUTHOR Robert G. Wilson v, Mar 31 2005 STATUS approved

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Last modified October 17 18:58 EDT 2019. Contains 328127 sequences. (Running on oeis4.)