A120377 Primes of the form 2*11^k-1.

241, 428717761

Offset: 1

Author

Walter Kehowski, Jun 28 2006

Keywords

• nonn
• hard
• bref

Comments

See comments for A057472. Examined in base 12, all n must be even and all primes must be 1-primes. For example, 241 is 181 in base 12.

The values of k < 1000 that yield primes are 2, 8, 248. - T. D. Noe, Nov 16 2006

Examples

			a(1) = 241 since 2*11^2-1 = 241 is the first prime.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..3

Crossrefs

Cf. A000043, A000668, A002957, A002959, A003307, A055558, A079363, A120378.

Programs

Maple

for w to 1 do for k from 1 to 2000 do n:=2*11^k-1; if isprime(n) then printf("%d, %d",k,n) fi od od;

Mathematica

Select[2*11^Range[1000]-1, PrimeQ] (* T. D. Noe, Nov 16 2006 *)

Formula

a(n) = n-th number such that 2*11^k-1 that is prime for some k.

a(n) = 2*11^A120378(n)-1. - R. J. Mathar, Mar 06 2010

Extensions

Corrected by T. D. Noe, Nov 16 2006