A102984 Numbers n such that 4*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 2, 4, 7, 22, 23, 80, 4427, 31319, 80150, 91144

Offset

1,3

Comments

Also numbers n such that (38*10^n-11)/9 is prime.

a(13) > 10^5. - Robert Price, May 08 2015

Links

Table of n, a(n) for n=1..12.

Makoto Kamada, Prime numbers of the form 422...221.

Index entries for primes involving repunits.

Formula

a(n) = A101719(n) + 1.

Mathematica

Do[ If[ PrimeQ[(38*10^n - 11)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101719.

Sequence in context: A306978 A337062 A153550 * A103017 A091833 A171978

Adjacent sequences: A102981 A102982 A102983 * A102985 A102986 A102987

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 22 2004

Extensions

a(10) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(1) = 0 from Robert Price, May 08 2015

a(11)-a(12) from Robert Price, May 08 2015

Status

approved