OFFSET
1,1
COMMENTS
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..26
FORMULA
a(n) = 2*6^A057472(n) - 1.
EXAMPLE
2*6^1 - 1 = 11, 2*6^2 - 1 = 71, 2*6^3 - 1 = 431, 2*6^4 - 1 = 2591 and 2*6^5 - 1 = 15551 are primes, but 2*6^6 - 1 = 93311 = 23*4057 is not.
MAPLE
A319535:= n-> (2*6^n-1): select(isprime, [seq((A319535(n), n=1..200))]); # K. D. Bajpai, Nov 15 2019
MATHEMATICA
Select[Table[2*6^k-1, {k, 1600}], PrimeQ[#]&] (* K. D. Bajpai, Nov 15 2019 *)
PROG
(PARI) for(n=1, 99, my(t); if(ispseudoprime(t=2*6^n-1), print1(t", ")))
(Magma) [k: n in [1..100] | IsPrime(k) where k is 2*6^n-1]; // K. D. Bajpai, Nov 15 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Jianing Song, Sep 22 2018
STATUS
approved