A128002 Numbers k such that (31^k - 1)/30 is prime.
7, 17, 31, 5581, 9973, 54493, 101111, 535571
Offset: 1
Links
- H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
- R. Fischer, Generalized repunit primes of the form (B^N-1)/(B-1).
- 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[(31^#-1)/30]&]
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PARI
is(n)=ispseudoprime((31^n-1)/30) \\ Charles R Greathouse IV, Feb 17 2017
Extensions
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008
a(7) = 101111 by Robert Price, Nov 26 2011
a(8) = 535571 from Alexander Zhirkov, added by Paul Bourdelais, Jan 28 2021
Missing term 54493 inserted at the suggestion of Eric Chen by Max Alekseyev, Aug 26 2023
Comments