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 A139484 Indices of Mersenne primes among primes of the form 24k + 7 (A107006). 7
 1, 2, 5, 129, 1536, 5430, 13138099 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 COMMENTS All Mersenne primes with the exception of the first one (3) are of the form 24*k + 7. Sequence lists indices m where A139483(m) is a Mersenne prime. LINKS Table of n, a(n) for n=2..8. EXAMPLE 5 is in this sequence, because A107006(5) is a Mersenne prime. MATHEMATICA w = {2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607}; Do[w[[n]] = 2^w[[n]] - 1, {n, 1, Length[w]}]; c = 0; a = {}; Do[k = 24 n + 7; If[PrimeQ[k], c = c + 1; If[MemberQ[w, k], AppendTo[a, c]]], {n, 1, 10000000}]; a With[{mps=2^#-1&/@MersennePrimeExponent[Range[20]]}, Position[ Select[ 24*Range[0, 10^8]+7, PrimeQ], _?(MemberQ[mps, #]&)]]//Flatten (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 20 2019 *) CROSSREFS Cf. A107006, A124477, A139479, A139483. Sequence in context: A175978 A092922 A093865 * A088271 A236045 A183128 Adjacent sequences: A139481 A139482 A139483 * A139485 A139486 A139487 KEYWORD nonn,hard,more AUTHOR Artur Jasinski, Apr 23 2008 EXTENSIONS Edited name and added example by Dmitry Kamenetsky, Jan 02 2011 a(8) from Charles R Greathouse IV, Mar 22 2011 STATUS approved

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Last modified April 24 20:08 EDT 2024. Contains 371963 sequences. (Running on oeis4.)