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 A127997 Numbers n such that (22^n - 1)/21 is prime. 9
 2, 5, 79, 101, 359, 857, 4463, 9029, 27823 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 9029 is a term found by Richard Fischer in 2004. - Alexander Adamchuk, Feb 11 2007 No other terms < 100000. - Robert Price, Feb 25 2012 LINKS H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930. H. Lifchitz, Mersenne and Fermat primes field Index to primes in various ranges, form ((k+1)^n-1)/k MATHEMATICA Select[Prime[Range[100]], PrimeQ[(22^#-1)/21]&] PROG (PARI) isok(n) = isprime((22^n-1)/21); \\ Michel Marcus, Mar 13 2016 CROSSREFS Sequence in context: A102983 A038583 A082080 * A096266 A123978 A303482 Adjacent sequences:  A127994 A127995 A127996 * A127998 A127999 A128000 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, Feb 11 2007 EXTENSIONS More terms from Ryan Propper, Mar 29 2007 27823 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008 STATUS approved

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Last modified December 8 14:38 EST 2019. Contains 329865 sequences. (Running on oeis4.)