A108966 Numbers n such that repunit(n) concatenated with its 10's complement is prime; or numbers n such that (1+7*10^n+100^n)/9 is prime.

1, 5, 16, 36, 61, 149, 725, 1104, 1276, 1289, 8575

Offset: 1

Author

Jason Earls, Jul 26 2005

Keywords

• base
• hard
• more
• nonn

Comments

Larger values are only Fermat and Lucas PRPs.

Examples

			a(2)=5 because 10^5-11111 = 88889 and 1111188889 is prime.
		

Crossrefs

Cf. A002275.