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 A309130 Smallest prime factor of A077586(n). 2
 7, 127, 2147483647, 170141183460469231731687303715884105727, 47, 338193759479, 231733529, 62914441, 2351, 1399, 295257526626031, 18287, 106937, 863, 4703, 138863, 22590223644617 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A263686 is a subsequence. Agrees with A263686 in the first four terms, but then the two sequences differ for the first time at n = 5, because prime(5) = 11 is not in A000043. a(18) = A263686(9) is greater than 1.56*10^17*(2^61-1), see link. a(n) = A077586(n) iff A077586(n) is prime, A077586(n) is prime for 1<=n<=4, but composite for 5<=n<=17. The status of A077586(18) = 2^(2^61-1)-1 is unknown. It is conjectured that A077586(n) is composite for all n>=5. a(20) = 456959, a(21) = 18384329, a(22) = 198839, a(23) = 2349023, a(24) = A263686(10) is greater than 1.25*10^16*(2^89-1). Conjecture: All terms are in A122094 (all terms in A263686 are in A122094). For examples related to that conjecture, see A322568. - Jeppe Stig Nielsen, Aug 29 2019 a(30) = 46559, a(32) = 23671, a(36) = 7151489, a(39) = 4698047, a(41) = 719, a(43) = 1440847, a(45) = 179689, a(47) = 11759383, a(48) = 23602441, a(50) = 9024439, a(51) = 28875361, a(52) = 6301423, a(54) = 2493983, a(56) = 33518137, a(59) = 6727783, a(66) = 95111, a(72) = 1439, a(73) = 99833, a(78) = 38119, a(81) = 26849, a(83) = 8258911, a(86) = 16173559, a(89) = 625343, a(93) = 9743. - Chai Wah Wu, Oct 16 2019 LINKS Double Mersennes Prime Search, History Eric Weisstein, Double Mersenne Number FORMULA a(n) = A020639(A077586(n)). CROSSREFS Cf. A077586, A263686. Sequence in context: A053713 A077586 A277634 * A263686 A002614 A187237 Adjacent sequences:  A309127 A309128 A309129 * A309131 A309132 A309133 KEYWORD nonn,hard,more,changed AUTHOR Richard N. Smith, Jul 13 2019 STATUS approved

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)