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A272057
Numbers n such that 3*4^n - 1 is prime.
2
1, 2, 3, 9, 17, 19, 32, 38, 47, 103, 108, 153, 162, 229, 235, 637, 1638, 2102, 2567, 6338, 7449, 12845, 20814, 40165, 61815, 77965, 117380, 207420, 351019, 496350, 600523, 1156367, 2117707, 5742009, 5865925, 5947859
OFFSET
1,2
COMMENTS
These are Williams primes to base 3.
Half of the even terms of A002235.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[3*4^# - 1] &]
PROG
(PARI) for(n=1, 10000, if(isprime(3*4^n-1), print1(n, ", ")))
KEYWORD
nonn,hard,more
AUTHOR
EXTENSIONS
a(25) corrected and a(33)-a(36) added by Giovanni Resta, Apr 19 2016, using data from A002235.
STATUS
approved