A128509 Initial prime, greater than 7, of a prime chain of length n under the iteration x -> 2x-7.

11, 13, 13, 367, 4987, 9697, 78007, 13356127, 13356127, 6753069187, 218617084627, 35679817649197, 92975416840027

Offset: 1

Author

Zak Seidov, May 07 2007

Keywords

• nonn
• more

Comments

From the definition we see that the sequence is monotonic (but not strictly) increasing. The sequence is a generalized Cunningham chain. - Stefan Steinerberger, May 12 2007

Examples

			a(2) = 13 because 13, 13*2-7=19 and 19*2-7=31 are primes.
		

Crossrefs

Cf. A057330, A084954.

Programs

Mathematica

k = 5; For[n = 2, n <= 10, n++, While[Union[PrimeQ[NestList[2# - 7 &, Prime[k], n]], PrimeQ[NestList[2# - 7 &, Prime[k], n]]] != {True}, k++ ]; Print[Prime[k]]] (* Stefan Steinerberger, May 12 2007 *)

Extensions

Edited by Stefan Steinerberger, May 12 2007

Edited by Don Reble, Nov 07 2007