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A163468
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Indices n such that half of n-th nonprime is prime
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0
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3, 4, 7, 9, 15, 18, 24, 27, 33, 43, 45, 54, 61, 64, 71, 80, 89, 93, 103, 109, 113, 122, 129, 139, 151, 157, 161, 168, 172, 179, 201, 208, 217, 220, 237, 241, 250, 261, 268, 279, 288, 291, 308, 311, 318, 321, 341, 361, 368, 371, 377, 388, 391, 408, 418, 428, 440
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Here n-th nonprime = A141468(n).
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FORMULA
| a(n)=2+A065897(n). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 01 2009]
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EXAMPLE
| If nonprime(3)=4 and 4/2=2=prime, then 3=a(1). If nonprime(4)=6 and 6/2=3=prime, then 4=a(2). If nonprime(7)=10 and 10/2=5=prime, then 7=a(3).
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MAPLE
| A141468 := proc(n) option remember ; if n = 1 then 0; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: for n from 1 to 600 do npr := A141468(n) ; if type(npr, 'even') then if isprime(npr/2) then printf("%d, ", n) ; fi; fi; od: [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 01 2009]
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CROSSREFS
| Cf. A065897, A000040, A141468.
Sequence in context: A008763 A005896 A147953 * A069183 A119907 A158911
Adjacent sequences: A163465 A163466 A163467 * A163469 A163470 A163471
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KEYWORD
| nonn,easy,less
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AUTHOR
| Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Jul 28 2009
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EXTENSIONS
| a(8) corrected by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 01 2009
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