Search: id:A002731
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%I A002731 M2444 N0971
%S A002731 3,5,9,11,15,19,25,29,35,39,45,49,51,59,61,65,69,71,79,85,95,101,
%T A002731 121,131,139,141,145,159,165,169,171,175,181,195,199,201,205,209,
%U A002731 219,221,231,245,261,271,275,279,289,299,309,315,321,325,329,335
%N A002731 Numbers n such that (n^2 + 1)/2 is prime.
%D A002731 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A002731 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002731 L. Euler, De numeris primis valde magnis (E283), reprinted in: Opera 
               Omnia. Teubner, Leipzig, 1911, Series (1), Vol. 3, p. 24.
%H A002731 T. D. Noe, <a href="b002731.txt">Table of n, a(n) for n=1..1000</a>
%t A002731 lst={};Do[If[PrimeQ[(n^2+1)/2], AppendTo[lst, n]], {n, 0, 10^4}];lst 
               [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Sep 10 2008]
%Y A002731 Equals 2*A027861(n-1)+1. A027862 gives primes, A091277 gives prime index.
%Y A002731 Sequence in context: A166699 A052092 A075991 this_sequence A006046 A161830 
               A151922
%Y A002731 Adjacent sequences: A002728 A002729 A002730 this_sequence A002732 A002733 
               A002734
%K A002731 nonn,easy,nice
%O A002731 1,1
%A A002731 N. J. A. Sloane (njas(AT)research.att.com).

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