A173472 Numbers k such that exactly one of prime(k)^2 - 2 and prime(k)^2 + 2 is prime.

1, 3, 4, 6, 8, 10, 12, 14, 15, 18, 20, 24, 27, 28, 31, 32, 34, 40, 43, 47, 48, 51, 52, 55, 62, 65, 68, 72, 82, 86, 87, 91, 94, 99, 100, 104, 107, 111, 119, 123, 128, 129, 130, 132, 133, 134, 135, 139, 141, 150, 152, 170, 172, 177, 180, 182, 191, 200, 202, 209, 211, 214

Offset: 1

Author

Juri-Stepan Gerasimov, Feb 19 2010

Keywords

• nonn
• less

Comments

Essentially the same as A137291.

Examples

			a(1)=1 because prime(1)^2 - 2 = 2 is prime and prime(1)^2 + 2 = 6 is composite.
		

Crossrefs

Cf. A137291.

Programs

Maple

isA173472 := proc(n) local p,pplus,pmin ; p := ithprime(n) ; pmin := isprime(p^2-2) ; pplus := isprime(p^2+2) ; if pmin <> pplus then return true; else return false; end if; end proc: for n from 1 to 300 do if isA173472(n) then printf("%d,",n) ; end if; end do ; # R. J. Mathar, Feb 21 2010

Extensions

More terms from R. J. Mathar, Feb 21 2010

Edited by Charles R Greathouse IV, Mar 24 2010