A103074 Numbers n such that 8*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 2, 3, 5, 17, 47, 177, 8462, 36615

Offset

1,2

Comments

Also numbers n such that (74*10^n-11)/9 is prime.

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

Links

Table of n, a(n) for n=1..9.

Makoto Kamada, Prime numbers of the form 822...221.

Index entries for primes involving repunits.

Formula

a(n) = A101061(n-1) + 1 for n>1.

Mathematica

Do[ If[ PrimeQ[(74*10^n - 11)/9], Print[n]], {n, 0, 10000}]

Prog

(PARI) for(n=0, 50000, if(isprime((74*10^n-11)/9), print1(n", "))) \\ Altug Alkan, Oct 13 2015

Crossrefs

Cf. A002275, A101061.

Sequence in context: A235630 A235636 A268130 * A173236 A268209 A245641

Adjacent sequences: A103071 A103072 A103073 * A103075 A103076 A103077

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(9) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Inserted a(1)=0 by Robert Price, Oct 13 2015

Status

approved