A127996 Numbers n such that (21^n - 1)/20 is prime.
3, 11, 17, 43, 271, 156217, 328129
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[(21^#-1)/20]&]
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PARI
is(n)=isprime((21^n-1)/20) \\ Charles R Greathouse IV, Feb 17 2017
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Prime95
PRP=1,21,328129,-1,0,0,"20"
Extensions
a(6)=156217 is a probable prime discovered by Paul Bourdelais, Apr 26 2010
a(7)=328129 is a probable prime discovered by Paul Bourdelais, Jun 02 2014