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Search: id:A002731
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| A002731 |
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Numbers n such that (n^2 + 1)/2 is prime.
(Formerly M2444 N0971)
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+0
6
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| 3, 5, 9, 11, 15, 19, 25, 29, 35, 39, 45, 49, 51, 59, 61, 65, 69, 71, 79, 85, 95, 101, 121, 131, 139, 141, 145, 159, 165, 169, 171, 175, 181, 195, 199, 201, 205, 209, 219, 221, 231, 245, 261, 271, 275, 279, 289, 299, 309, 315, 321, 325, 329, 335
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
L. Euler, De numeris primis valde magnis (E283), reprinted in: Opera Omnia. Teubner, Leipzig, 1911, Series (1), Vol. 3, p. 24.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..1000
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MATHEMATICA
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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]
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CROSSREFS
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Equals 2*A027861(n-1)+1. A027862 gives primes, A091277 gives prime index.
Sequence in context: A166699 A052092 A075991 this_sequence A006046 A161830 A151922
Adjacent sequences: A002728 A002729 A002730 this_sequence A002732 A002733 A002734
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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