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Search: id:A154862
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| A154862 |
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Nonprimes of the form: prime(prime(n)) - 2*n. |
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+0
1
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| 1, 1, 9, 21, 45, 51, 65, 105, 133, 153, 209, 243, 247, 325, 357, 385, 413, 459, 495, 531, 675, 707, 729, 789, 805, 845, 891, 913, 951, 981, 1003, 1067, 1083, 1111, 1125, 1203, 1313, 1335, 1347, 1369, 1395, 1417, 1557, 1625, 1703, 1725, 1935, 1967, 2133, 2211
(list; graph; listen)
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OFFSET
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1,3
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EXAMPLE
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If n=1 and prime(prime(1))-2*1=prime(2)-2=3-2=1(nonprime), then 1=a(1). If n=2 and prime(prime(2))-2*2=prime(3)-4=5-4=1(nonprime), then 1=a(2). if n=3, then prime(prime(3))-2*3=prime(5)-6=11-6=5(prime). If n=4 and prime(prime(4))-2*4=prime(7)-8=17-8=9(nonprime), then 9=a(3), etc.
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MAPLE
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for n from 1 to 100 do p := ithprime(ithprime(n))-2*n ; if not isprime(p) then printf("%d, ", p) ; fi; od: [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 18 2009]
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CROSSREFS
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Cf. A006450,A141468.
Sequence in context: A053476 A110680 A163205 this_sequence A020137 A020190 A135187
Adjacent sequences: A154859 A154860 A154861 this_sequence A154863 A154864 A154865
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KEYWORD
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nonn
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AUTHOR
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Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Jan 16 2009
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EXTENSIONS
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Replaced 35 by 45. Replaced 645 by 675. R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 18 2009
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