A063898 Smallest k > 0 such that k + F_n are all primes, where F_n is the n-th Fermat number.

2, 2, 2, 14, 14, 14, 66746, 475424, 12124166, 14899339904

Offset

0,1

Comments

Is this sequence finite?

Links

Table of n, a(n) for n=0..9.

Example

For j=3 a(3)=2 because 257+2, 17+2, 5+2, 3+2 are all primes.
For j=4 a(4)=14 because 65537+14, 257+14, 17+14, 5+14, 3+14 are all primes.

Prog

(PARI) okprimep(mink, vecf) = {for (i=1, #vecf, if (! isprime(mink + vecf[i]), return (0)); ); return (1); }
a(n) = {mink = 1; vecf = vector(n+1, i, 2^(2^(i-1)) + 1); while (! okprimep(mink, vecf), mink++); mink; } \\ Michel Marcus, Sep 28 2013

Crossrefs

Cf. A000215 (Fermat numbers).

Sequence in context: A369077 A183584 A289068 * A074052 A350599 A361815

Adjacent sequences: A063895 A063896 A063897 * A063899 A063900 A063901

Keyword

hard,more,nonn

Author

Felice Russo, Aug 29 2001

Extensions

a(10) from Donovan Johnson, Oct 12 2008

Status

approved