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 A128005 Numbers n such that (40^n - 1)/39 is prime. 11
 2, 5, 7, 19, 23, 29, 541, 751, 1277 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS No other terms for n < 100000. - Robert Price, Jan 27 2012 LINKS Table of n, a(n) for n=1..9. 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[(40^#-1)/39]&] PROG (PARI) isok(n) = isprime((40^n-1)/39); \\ Michel Marcus, Mar 13 2016 CROSSREFS Sequence in context: A097052 A102937 A045358 * A045359 A042809 A002531 Adjacent sequences: A128002 A128003 A128004 * A128006 A128007 A128008 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, Feb 11 2007 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008 STATUS approved

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Last modified May 30 17:56 EDT 2024. Contains 372971 sequences. (Running on oeis4.)