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 A127995 Numbers n such that (20^n - 1)/19 is prime. 23
 3, 11, 17, 1487, 31013, 48859, 61403, 472709 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS P. Bourdelais, A Generalized Repunit Conjecture H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930. H. Lifchitz, Mersenne and Fermat primes field MATHEMATICA Select[Prime[Range[100]], PrimeQ[(20^#-1)/19]&] PROG (Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 05 2010] (Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 08 2010] CROSSREFS Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035, A127996, A127997, A127998, A127999, A128000, A098438, A128002, A128003, A128004, A128005. Sequence in context: A128346 A128031 A194128 * A119141 A225144 A228470 Adjacent sequences:  A127992 A127993 A127994 * A127996 A127997 A127998 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, Feb 11 2007 EXTENSIONS One more term from Ryan Propper, Mar 29 2007 a(5) & a(6) are probable primes found by Paul Bourdelais, Mar 05 2010 a(7) is a probable prime found by Paul Bourdelais, Mar 08 2010 a(8) is a probable prime found by Paul Bourdelais, Jan 15 2015 STATUS approved

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Last modified November 25 12:53 EST 2015. Contains 264417 sequences.