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A173444 Either (n-th prime-1)^2-+1, but not both, is prime. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that either A005722(n)-+1 is prime.

LINKS

Table of n, a(n) for n=1..60.

EXAMPLE

1 is in the sequence because (1st prime-1)^2-1=0 is nonprime and (1st prime-1)^2+1=2 is prime;

3 is in the sequence because (3rd prime-1)^2-1=15 is nonprime and (3rd prime-1)^2+1=17 is prime.

MAPLE

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: # R. J. Mathar, Apr 24 2010

MATHEMATICA

ppQ[n_]:=Module[{c=(Prime[n]-1)^2}, Sort[PrimeQ[{c+1, c-1}]]== {False, True}]; Select[Range[400], ppQ] (* Harvey P. Dale, Jun 24 2011 *)

CROSSREFS

Cf. A000040, A005722, A006093, A127435.

Sequence in context: A023713 A032890 A092859 * A120424 A139440 A102607

Adjacent sequences:  A173441 A173442 A173443 * A173445 A173446 A173447

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Feb 18 2010, Mar 27 2010

EXTENSIONS

More terms from R. J. Mathar, Apr 24 2010

Definition clarified by Harvey P. Dale, Jun 24 2011

STATUS

approved

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Last modified September 20 03:55 EDT 2019. Contains 327212 sequences. (Running on oeis4.)