A103107 Numbers n such that 9*10^n + 8*R_n - 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 6, 9, 90, 111, 210, 237, 414, 1192, 1260, 5836, 6772, 24861, 52431

Offset

1,2

Comments

Also numbers n such that (89*10^n-71)/9 is prime.

a(15) > 10^5. - Robert Price, Nov 12 2015

Links

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

Makoto Kamada, Prime numbers of the form 988...881.

Index entries for primes involving repunits.

Formula

a(n) = A101016(n-1) + 1, for n > 1.

Mathematica

Do[ If[ PrimeQ[(89*10^n - 71)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101016.

Sequence in context: A266006 A372412 A377680 * A370623 A377683 A121233

Adjacent sequences: A103104 A103105 A103106 * A103108 A103109 A103110

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(13) from Kamada data by Robert Price, Dec 14 2010

Inserted a(1) = 0 and added a(14) from Robert Price, Nov 12 2015

Status

approved