A186521 Numbers n>0 such that (7*10^(n+2)+666)*10^n+7 is prime.

1, 3, 6, 7, 49, 578, 793, 1322, 1392, 2392, 3066, 13479

Offset: 1

Author

Arkadiusz Wesolowski, Feb 23 2011

Keywords

• nonn
• base
• more

Comments

Or, indices of primes in A046720. Rudolf Ondrejka calls these "beastly palindromic primes".

Some of the larger entries may only correspond to probable primes.

Links

• Chris Caldwell, The Prime Glossary, Beastly prime
• G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 76667
• R. Ondrejka, The Top Ten: a Catalogue of Primal Configurations

Crossrefs

Cf. A046720, A186086.

Programs

Mathematica

Select[Range[10^3], PrimeQ[(7*10^(# + 2) + 666)*10^# + 7] &] (* Arkadiusz Wesolowski, Sep 08 2011 *)

Extensions

a(12) added by Arkadiusz Wesolowski, Mar 16 2011