A103097 Numbers k such that 9*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

2, 4, 8, 2960, 4571, 5201, 17864, 21922, 89375, 147676

Offset

1,1

Comments

Also numbers n such that (85*10^n-31)/9 is prime.

a(10) > 10^5. - Robert Price, Nov 07 2015

Links

Table of n, a(n) for n=1..10.

Makoto Kamada, Prime numbers of the form 944...441.

Index entries for primes involving repunits.

Formula

a(n) = A101006(n) + 1.

Mathematica

Do[ If[ PrimeQ[(85*10^n - 31)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101006.

Sequence in context: A012456 A071686 A296742 * A389794 A335750 A062286

Adjacent sequences: A103094 A103095 A103096 * A103098 A103099 A103100

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(7)-a(8) from Kamada data by Robert Price, Dec 14 2010

a(9) from Robert Price, Nov 07 2015

a(10) from Kamada link by Tyler Busby, Sep 04 2025

Status

approved