A272057 - OEIS

A272057

Numbers n such that 3*4^n - 1 is prime.

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

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OFFSET

1,2

COMMENTS

These are Williams primes to base 3.

Half of the even terms of A002235.

LINKS

Table of n, a(n) for n=1..36.

H. C. Williams, The primality of certain integers of the form 2Ar^n - 1, Acta Arith. 39 (1981), 7-17.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[3*4^# - 1] &]

PROG

(PARI) for(n=1, 10000, if(isprime(3*4^n-1), print1(n, ", ")))

CROSSREFS

Cf. A002235, A000043, A003307, A046865, A079906, A046866, A268061, A268356, A056725, A046867, A079907.

Sequence in context: A156066 A143890 A270339 * A056658 A302164 A295965

Adjacent sequences: A272054 A272055 A272056 * A272058 A272059 A272060

KEYWORD

nonn,hard,more

AUTHOR

Tim Johannes Ohrtmann, Apr 19 2016

EXTENSIONS

a(25) corrected and a(33)-a(36) added by Giovanni Resta, Apr 19 2016, using data from A002235.

STATUS

approved