A129842 Primes p such that (p^2 - 3p - 2)/2 is prime.

7, 11, 19, 23, 31, 43, 47, 67, 79, 83, 107, 127, 151, 167, 199, 211, 227, 239, 251, 271, 283, 307, 359, 419, 431, 439, 443, 467, 479, 523, 547, 563, 587, 599, 643, 647, 719, 743, 827, 859, 883, 887, 947, 991, 1031, 1039, 1103, 1171, 1259, 1303, 1399, 1423

Offset: 1

Author

J. M. Bergot, May 22 2007

Keywords

• nonn

Comments

These primes are all of the form 4k+3 (cf. A002145, A080148). - R. J. Mathar, Jun 08 2007

Examples

			For p = 31, one half of 31^2 - 3*31 - 2 equals 433, which is prime.
		

Links

• Max Alekseyev, Table of n, a(n) for n=1..230

Programs

Maple

a:=proc(n) local b: b:=ithprime(n): if isprime((b^2-3*b-2)/2)=true then b else fi end: seq(a(n),n=1..300); # Emeric Deutsch, May 25 2007
isA129842 := proc(p) if isprime(p) then isprime((p^2-3*p-2)/2) ; else false ; fi ; end: for n from 1 to 880 do p := ithprime(n) : if isA129842(p) then printf("%d, ",p) ; fi ; od : # R. J. Mathar, Jun 08 2007

Mathematica

Select[Prime[Range[2, 224]], PrimeQ[(#^2 - 3*# - 2)/2] &] (* Stefan Steinerberger, Jun 23 2007 *)

Extensions

More terms from Emeric Deutsch and R. J. Mathar, May 25 2007