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A056561
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Numbers n such that n^2 + n + 41 is prime.
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9
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 42, 43, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 77, 78
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Among first 100000 terms, the only run of 13 subsequent values >39 is 219..231. [From Zak Seidov (zakseidov(AT)yahoo.com), Jan 28 2009]
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REFERENCES
| P. Hoffman, Archimedes' Revenge, pp. 39-40,Penguin Books 1988.
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LINKS
| Zak Seidov, Table of n, a(n) for n = 1..10000.
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FORMULA
| a(n) =(sqrt(4*A005846(n)-163)-1)/2
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EXAMPLE
| 39 is in the sequence because 39^2+39+41=1601 which is prime but 40 is not because 40^2+40+41=1681=41*41
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CROSSREFS
| Cf. A002837, A005846, A007634.
Sequence in context: A180925 A083243 A002837 * A174670 A178772 A085735
Adjacent sequences: A056558 A056559 A056560 * A056562 A056563 A056564
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KEYWORD
| nonn
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AUTHOR
| Henry Bottomley (se16(AT)btinternet.com), Jun 26 2000
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