A164621 Primes p such that p*floor(p/2)-2 and p*floor(p/2)+2 are also prime numbers.

7, 31, 79, 211, 271, 751, 787, 1231, 1447, 1459, 2347, 2551, 3727, 5119, 6427, 6691, 8467, 8707, 9007, 10099, 10531, 10567, 10831, 11959, 18691, 21487, 22039, 22567, 23059, 23167, 23371, 24379, 24499, 25171, 26371, 27967, 28579, 28591, 29287

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Aug 17 2009

Keywords

• nonn

Examples

			7*3-2=13, 7*3+2=17,..
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A068229, A158708, A164620

Programs

Mathematica

lst={};Do[p=Prime[n];If[PrimeQ[p*Floor[p/2]-2]&&PrimeQ[p*Floor[p/2]+2],AppendTo[lst,p]],{n,2*7!}];lst
Select[Prime[Range[3200]],AllTrue[# Floor[#/2]+{2,-2},PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 04 2020 *)