A103109 Numbers n such that 9*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 3, 4, 6, 9, 12, 16, 34, 129, 243, 252, 529, 4885, 6363, 12951, 13188, 29931, 34888, 49516, 67431, 77781

Offset

1,2

Comments

Also numbers n such that (89*10^n-17)/9 is prime.

a(22) > 10^5. - Robert Price, Nov 14 2015

Links

Table of n, a(n) for n=1..21.

Makoto Kamada, Prime numbers of the form 988...887.

Index entries for primes involving repunits.

Formula

a(n) = A101018(n) + 1.

Mathematica

Do[ If[ PrimeQ[(89*10^n - 17)/9], Print[n]], {n, 0, 10000}]

Prog

(PARI) is(n)=isprime(9*10^n + 8*(10^n-1)/9 - 1) \\ Anders Hellström, Nov 14 2015

Crossrefs

Cf. A002275, A101018.

Sequence in context: A202171 A182531 A097922 * A241639 A241655 A288346

Adjacent sequences: A103106 A103107 A103108 * A103110 A103111 A103112

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(15)-a(18) from Kamada data by Robert Price, Dec 14 2010

a(19) from Erik Branger May 01 2013 by Ray Chandler, Aug 17 2013

a(20)-a(21) from Robert Price, Nov 14 2015

Status

approved