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A064213 Least k such that k*3^n +- 1 are twin primes. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

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

MATHEMATICA

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

PROG

(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

CROSSREFS

Cf. A063983.

Sequence in context: A021707 A126560 A289762 * A245518 A217462 A016510

Adjacent sequences:  A064210 A064211 A064212 * A064214 A064215 A064216

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Sep 21 2001

EXTENSIONS

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

STATUS

approved

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Last modified November 14 15:19 EST 2019. Contains 329126 sequences. (Running on oeis4.)