Search: id:A090872
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%I A090872
%S A090872 2,2,2,2,2,7072833120,2072005925466
%N A090872 a(n) is the smallest number m greater than 1 such that m^(2^k)+1 for 
               k=0,1,...,n are primes.
%C A090872 The first five terms of this sequence correspond to Fermat primes.
%H A090872 C. Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_137.htm">
               Puzzle 137. Product of primes + 1, a square</a>.
%H A090872 C. Rivera (ed.), <a href="http://primepuzzles.net/puzzles/puzz_399.htm">
               Prime Puzzle # 399</a>.
%e A090872 a(5)=7072833120 because 7072833120^2^k+1 for k=0,1,2,3,4,5 are primes.
%Y A090872 Cf. A019434, A000215.
%Y A090872 Cf. A090873-A090875.
%Y A090872 Sequence in context: A056993 A057331 A067089 this_sequence A063473 A096859 
               A005086
%Y A090872 Adjacent sequences: A090869 A090870 A090871 this_sequence A090873 A090874 
               A090875
%K A090872 nonn
%O A090872 0,1
%A A090872 Farideh Firoozbakht (f.firoozbakht(AT)sci.ui.ac.ir), Jan 31 2004
%E A090872 a(6) from Jens Kruse Andersen (jens.k.a(AT)get2net.dk), May 06 2007

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