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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
2, 2, 2, 2, 2, 7072833120, 2072005925466 (list; graph; refs; listen; history; text; internal format)
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. A090873-A090875.

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

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Last modified June 6 11:14 EDT 2020. Contains 334827 sequences. (Running on oeis4.)