A064812 Smallest prime p such that the infinite sequence {p, p'=2p-1, p''=2p'-1, ...} begins with a string of exactly n primes.

5, 3, 2, 2131, 1531, 33301, 16651, 15514861, 857095381, 205528443121, 1389122693971, 216857744866621, 758083947856951, 107588900851484911, 69257563144280941

Offset

1,1

Comments

Chains of length n of nearly doubled primes.

Smallest prime beginning a complete Cunningham chain of length n of the second kind. (For the first kind see A005602.) - Jonathan Sondow, Oct 30 2015

Links

Table of n, a(n) for n=1..15.

G. Löh, Long chains of nearly doubled primes, Math. Comp., 53 (1989), 751-759.

Wikipedia, Cunningham chain

Example

a(3) = 2 because 2 is the smallest prime such that the sequence {2, 3, 5, 9, ...} begins with exactly 3 primes, where each term in the sequence is twice the preceding term minus 1.

Crossrefs

A better version of A005603.

Cf. (A005382 and A005383), A057326, A057327, A057328, A057329, A057330, A005602.

Cf. A002808, A006450, A049076-A049081, A050436, A076237-A076239, A050436-A050439, A065860, A181697, A263879.

Sequence in context: A193799 A262225 A330092 * A282469 A216998 A346469

Adjacent sequences: A064809 A064810 A064811 * A064813 A064814 A064815

Keyword

nonn,changed

Author

David Terr, Oct 21 2002

Status

approved