A127995 Numbers k such that (20^k - 1)/19 is prime.
3, 11, 17, 1487, 31013, 48859, 61403, 472709, 984349
Offset: 1
Links
- Paul Bourdelais, A Generalized Repunit Conjecture
- 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
Programs
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Mathematica
Select[Prime[Range[100]],PrimeQ[(20^#-1)/19]&]
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PARI
is(n)=isprime((20^n-1)/19) \\ Charles R Greathouse IV, Feb 17 2017
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
a(9) from Paul Bourdelais, Sep 13 2021