A064213 Least k such that k*3^n +- 1 are twin primes.

4, 2, 2, 4, 10, 40, 58, 64, 28, 24, 8, 210, 70, 36, 12, 4, 78, 26, 28, 20, 90, 30, 10, 630, 210, 70, 82, 416, 612, 204, 68, 930, 310, 406, 1078, 1164, 388, 176, 190, 334, 190, 726, 242, 1004, 398, 1430, 1372, 2730, 910, 1560, 520

Offset: 0

Author

Robert G. Wilson v, Sep 21 2001

Keywords

• nonn

Comments

k must be even because 3^n is odd. - Harry J. Smith, Sep 10 2009

Links

• Harry J. Smith, Table of n, a(n) for n = 0..225

Crossrefs

Cf. A063983.

Programs

Mathematica

Do[ k = 1; While[ ! PrimeQ[ k*3^n + 1 ] || ! PrimeQ[ k*3^n - 1 ], k++ ]; Print[ k ], {n, 0, 50} ]

PARI

{ for (n=0, 225, k=0; p=3^n; until (isprime(k*p - 1) && isprime(k*p + 1), k+=2); write("b064213.txt", n, " ", k); ) } \\ Harry J. Smith, Sep 10 2009

Extensions

Offset changed from 1 to 0 by Harry J. Smith, Sep 10 2009