A103026 Numbers n such that 6*10^n+7 is prime.

0, 1, 2, 3, 8, 9, 19, 58, 121, 187, 806, 855, 1019, 2593, 2749, 3016, 4295, 9664, 14927, 34562, 64387, 71299, 71951

Offset

1,3

Comments

a(24) > 2*10^5. - Robert Price, Sep 17 2015

Links

Table of n, a(n) for n=1..23.

Makoto Kamada, Prime numbers of the form 600...007.

Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.

Formula

a(n) = A101518(n-1) + 1 for n>1. - L. Edson Jeffery, Nov 28 2013

Mathematica

Do[ If[ PrimeQ[6*10^n + 7], Print[n]], {n, 0, 10000}]

Prog

(PARI) is(n)=ispseudoprime(6*10^n+7) \\ Charles R Greathouse IV, Jun 12 2017

Crossrefs

Cf. A101518.

Sequence in context: A309017 A247375 A282508 * A098506 A279090 A163168

Adjacent sequences: A103023 A103024 A103025 * A103027 A103028 A103029

Keyword

nonn,more,hard

Author

Robert G. Wilson v, Jan 18 2005

Extensions

a(19)-a(23) from Kamada link by Ray Chandler, Jan 04 2011

Inserted a(1)=0 by Robert Price, Sep 17 2015

Status

approved