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A028870
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Numbers n such that n^2 - 2 is prime.
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19
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2, 3, 5, 7, 9, 13, 15, 19, 21, 27, 29, 33, 35, 37, 43, 47, 49, 55, 61, 63, 69, 71, 75, 77, 89, 93, 103, 107, 117, 119, 121, 127, 131, 135, 139, 145, 155, 161, 169, 173, 177, 183, 191, 205, 211, 217, 223, 231, 233, 237, 239, 247, 253, 257, 259, 265, 267, 273, 279, 285
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| It is conjectured that this sequence is infinite.
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REFERENCES
| D. Shanks, Solved and Unsolved Problems in Number Theory, 2nd. ed., Chelsea, 1978, p. 31.
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LINKS
| Nathaniel Johnston, Table of n, a(n) for n = 1..10000
P. De Geest, Palindromic Quasipronics of the form n(n+x)
Eric Weisstein's World of Mathematics, Near-Square Prime
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EXAMPLE
| 5^2 - 2 = 23 is prime, so 5 is in the sequence.
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MATHEMATICA
| a[n_]:=n^x-y; lst={}; x=2; y=2; Do[If[PrimeQ[a[n]], AppendTo[lst, n]], {n, 0, 6!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Jan 03 2009]
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PROG
| (MAGMA) [n: n in [1..1000] |IsPrime( n^2 - 2)] [From V. Librandi, Nov 18 2010]
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CROSSREFS
| Cf. A028871.
Sequence in context: A102424 A080000 A032459 * A057886 A200672 A069999
Adjacent sequences: A028867 A028868 A028869 * A028871 A028872 A028873
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KEYWORD
| nonn
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AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com)
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