A102999 Numbers n such that 4*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 2, 7, 14, 25, 116, 427, 595, 637, 776, 1706, 16628, 55558

Offset

1,3

Comments

Also numbers n such that (44*10^n-17)/9 is prime.

a(15) > 10^5. - Robert Price, Jun 05 2015

Links

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 488...887.

Index entries for primes involving repunits.

Formula

a(n) = A101736(n) + 1.

Mathematica

Do[ If[ PrimeQ[(44*10^n - 17)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101736.

Sequence in context: A088207 A194111 A343859 * A225277 A367954 A333644

Adjacent sequences: A102996 A102997 A102998 * A103000 A103001 A103002

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 17 2005

Extensions

Addition of a(13) from Kamada data by Robert Price, Dec 13 2010

a(14) from Robert Price, Jun 05 2015

Prepended a(1) = 0 by Robert Price, Jun 05 2015

Status

approved