

A090872


a(n) is the smallest number m greater than 1 such that m^(2^k)+1 for k=0,1,...,n are primes.


5




OFFSET

0,1


COMMENTS

The first five terms of this sequence correspond to Fermat primes.


LINKS

Table of n, a(n) for n=0..6.
C. Rivera, Puzzle 137. Product of primes + 1, a square.
C. Rivera (ed.), Prime Puzzle # 399.


EXAMPLE

a(5)=7072833120 because 7072833120^2^k+1 for k=0,1,2,3,4,5 are primes.


CROSSREFS

Cf. A019434, A000215.
Cf. A090873A090875.
Sequence in context: A057331 A270374 A067089 * A283472 A225538 A212355
Adjacent sequences: A090869 A090870 A090871 * A090873 A090874 A090875


KEYWORD

nonn


AUTHOR

Farideh Firoozbakht, Jan 31 2004


EXTENSIONS

a(6) from Jens Kruse Andersen, May 06 2007


STATUS

approved



