A103049 Numbers n such that 7*10^n-3 is prime.

1, 3, 4, 6, 10, 20, 51, 138, 190, 360, 378, 393, 1384, 1594, 2759, 2868, 5395, 7494, 10491, 11199, 12190, 33594, 38256, 89169, 165916

Offset

1,2

Comments

Also numbers n such that 6*10^n + 9*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

a(26) > 2*10^5. - Robert Price, Aug 17 2015

Links

Table of n, a(n) for n=1..25.

Makoto Kamada, Prime numbers of the form 699...997.

Index entries for primes involving repunits.

Formula

a(n) = A101542(n) + 1.

Mathematica

Do[ If[ PrimeQ[7*10^n - 3], Print[n]], {n, 0, 10000}]

Prog

(PARI) is(n)=ispseudoprime(7*10^n-3) \\ Charles R Greathouse IV, Jun 12 2017

Crossrefs

Cf. A002275, A101542.

Sequence in context: A353138 A052548 A232268 * A103016 A061032 A091424

Adjacent sequences: A103046 A103047 A103048 * A103050 A103051 A103052

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

a(19)-a(24) from Kamada data by Robert Price, Dec 14 2010

a(25) from Robert Price, Aug 17 2015

Status

approved