A103078 Numbers n such that 8*10^n + 3*R_n + 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 4, 9, 10, 15, 44, 55, 56, 124, 140, 279, 674, 848, 1420, 1462, 3314, 3442, 4141, 35625

Offset

1,2

Comments

Also numbers n such that (25*10^n+17)/3 is prime.

a(21) > 10^5. - Robert Price, Oct 20 2015

Links

Table of n, a(n) for n=1..20.

Makoto Kamada, Prime numbers of the form 833...339.

Index entries for primes involving repunits.

Formula

a(n) = A101065(n) + 1.

Mathematica

Do[ If[ PrimeQ[(25*10^n + 17)/3], Print[n]], {n, 0, 10000}]

Prog

(PARI) for(n=1, 1e3, if(isprime((25*10^n+17)/3), print1(n", "))) \\ Altug Alkan, Oct 20 2015

Crossrefs

Cf. A002275, A101065.

Sequence in context: A287413 A026602 A287436 * A060756 A075347 A352506

Adjacent sequences: A103075 A103076 A103077 * A103079 A103080 A103081

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(20) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved