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

1,1

Links

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

Example

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

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 *)

Crossrefs

Cf. A068229, A158708, A164620

Sequence in context: A107006 A107005 A201477 * A202254 A305290 A262012

Adjacent sequences: A164618 A164619 A164620 * A164622 A164623 A164624

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Aug 17 2009

Status

approved