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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
H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
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
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.)