A103035 Numbers n such that 6*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 2, 5, 6, 11, 15, 69, 90, 134, 189, 245, 267, 270, 470, 1575, 2295, 2507, 3512, 3825, 6857, 11022, 11657, 17499, 35036, 41966, 50558, 93062

Offset

1,2

Comments

Also numbers n such that (58*10^n-13)/9 is prime.

a(28) > 10^5. - Robert Price, Sep 12 2015

Links

Table of n, a(n) for n=1..27.

Makoto Kamada, Prime numbers of the form 644...443.

Index entries for primes involving repunits.

Formula

a(n) = A101528(n-1) + 1 for n>1.

Mathematica

Do[ If[ PrimeQ[(58*10^n - 13)/9], Print[n]], {n, 0, 10000}]

Prog

(PARI) is(n)=isprime(6*10^n + 4*(10^n-1)/9 - 1) \\ Anders Hellström, Sep 12 2015

Crossrefs

Cf. A002275, A101528.

Sequence in context: A336527 A293398 A180323 * A088273 A049054 A319140

Adjacent sequences: A103032 A103033 A103034 * A103036 A103037 A103038

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

a(21)-a(23) from Kamada data by Robert Price, Dec 14 2010

a(24)-a(25) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Inserted a(1)=0 by Robert Price, Sep 12 2015

a(26)-a(27) from Robert Price, Sep 12 2015

Status

approved