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A173444
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Either (n-th prime-1)^2-+1, but not both, is prime.
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1
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1, 3, 4, 5, 7, 12, 13, 19, 31, 32, 36, 37, 42, 47, 53, 54, 55, 58, 60, 63, 78, 79, 82, 83, 91, 94, 102, 105, 106, 118, 125, 126, 133, 135, 144, 155, 156, 159, 161, 163, 178, 184, 190, 206, 210, 214, 216, 219, 247, 248, 284, 286, 288, 307, 313, 315, 322, 336, 340, 344
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OFFSET
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1,2
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COMMENTS
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Numbers n such that either A005722(n)-+1 is prime.
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LINKS
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Table of n, a(n) for n=1..60.
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EXAMPLE
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a(1)=1 because (1th prime-1)^2-1=0=nonprime and (1th prime-1)^2+1=2=prime; a(2)=3 because (3th prime-1)^2-1=15=nonprime and (3th prime-1)^2+1=17=prime.
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MAPLE
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A005722 := proc(n) (ithprime(n)-1)^2 ; end proc: for n from 1 to 800 do a := A005722(n) ; if isprime(a-1) <> isprime(a+1) then printf("%d, ", n) ; end if; end do: [From R. J. Mathar, Apr 24 2010]
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MATHEMATICA
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ppQ[n_]:=Module[{c=(Prime[n]-1)^2}, Sort[PrimeQ[{c+1, c-1}]]== {False, True}]; Select[Range[400], ppQ] (* From Harvey P. Dale, June 24 2011 *)
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CROSSREFS
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Cf. A000040, A005722, A006093, A127435.
Sequence in context: A023713 A032890 A092859 * A120424 A139440 A102607
Adjacent sequences: A173441 A173442 A173443 * A173445 A173446 A173447
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KEYWORD
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nonn
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AUTHOR
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Juri-Stepan Gerasimov, Feb 18 2010, Mar 27 2010
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EXTENSIONS
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More terms from R. J. Mathar, Apr 24 2010
Definition clarified by Harvey P. Dale, June 24 2011
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STATUS
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approved
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