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A168079
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Numbers n such that exactly one of n+-1, n+-2 and n+-3 is prime.
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1
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-1, 7, 11, 13, 17, 19, 24, 25, 27, 29, 31, 33, 35, 36, 41, 43, 48, 49, 51, 52, 54, 55, 57, 59, 61, 63, 65, 66, 71, 73, 75, 77, 78, 84, 85, 87, 88, 90, 91, 92, 94, 95, 96, 101, 103, 107, 109, 114, 115, 116, 124, 125, 126, 132, 133, 135, 137, 139, 141, 142, 146, 147, 149
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OFFSET
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1,2
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LINKS
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FORMULA
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EXAMPLE
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a(1)=-1 (-4,-3,-2,0 and 1 are nonprimes, 2 is prime);
a(2)=7 (4,6,8,9 and 10 are nonprimes, 5 is prime);
a(3)=13 (8,9,10,12 and 14 are nonprimes, 11 is prime).
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MATHEMATICA
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f[n_] := Length[Select[Drop[Range[n - 3, n + 3], {4}], PrimeQ]] == 1; Join[{-1}, Select[Range[0, 200], f]] (* G. C. Greubel, Jul 09 2016 *)
Join[{-1}, Select[Range[200], Total[Boole[PrimeQ[Drop[Range[#-3, #+3], {4}]]]]==1&]] (* Harvey P. Dale, Oct 16 2018 *)
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PROG
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(PARI) is(n)=isprime(n-3) + isprime(n-2) + isprime(n-1) + isprime(n+1) + isprime(n+2) + isprime(n+3) == 1 \\ Charles R Greathouse IV, Jun 13 2017
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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EXTENSIONS
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Corrected (11, 57 inserted, 16 replaced by 126) by R. J. Mathar, Jun 04 2010
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STATUS
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approved
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