A103066 Numbers n such that 7*10^n + 8*R_n - 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 3, 6, 60, 288, 1314, 1728, 2493, 13893, 13944, 17100, 70227

Offset

1,3

Comments

Also numbers n such that (71*10^n-53)/9 is prime.

a(14) > 10^5. - Robert Price, Oct 06 2015

Links

Table of n, a(n) for n=1..13.

Makoto Kamada, Prime numbers of the form 788...883.

Index entries for primes involving repunits.

Formula

a(n) = A101151(n-1) + 1 for n>1.

Example

For n=0, (71*10^n-53)/9 = 2 which is prime.

Mathematica

Do[ If[ PrimeQ[(71*10^n - 53)/9], Print[n]], {n, 0, 10000}]

Prog

(PARI) for(n=0, 10^5, if(isprime((71*10^n-53)/9), print1(n", "))); \\ Altug Alkan, Oct 06 2015

Crossrefs

Cf. A002275, A101151.

Sequence in context: A012473 A058161 A012877 * A145887 A364852 A219809

Adjacent sequences: A103063 A103064 A103065 * A103067 A103068 A103069

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(10)-a(12) from Kamada data by Robert Price, Dec 14 2010

Inserted a(1)=0 and added a(13) by Robert Price, Oct 06 2015

Status

approved