A164620 Primes p such that 1 +p*floor(p/2) is also prime.

2, 5, 13, 17, 41, 61, 89, 97, 101, 113, 149, 173, 229, 241, 281, 317, 349, 353, 373, 397, 409, 421, 433, 461, 509, 521, 661, 673, 761, 853, 881, 937, 941, 1013, 1093, 1109, 1249, 1289, 1297, 1373, 1433, 1549, 1741, 1753, 1913, 2113, 2213, 2269, 2281, 2297

Offset

1,1

Links

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

Example

p=2 qualifies since 2*1+1=3 is prime. p=5 qualifies since 5*2+1=11 is prime.

Mathematica

lst={}; Do[p=Prime[n]; If[PrimeQ[p*Floor[p/2]+1], AppendTo[lst, p]], {n, 3*6!}]; lst
Select[Prime[Range[350]], PrimeQ[1+#*Floor[#/2]]&] (* Harvey P. Dale, Apr 07 2015 *)

Crossrefs

Cf. A008846, A020882, A158708.

Sequence in context: A102854 A156009 A215275 * A333876 A156013 A112634

Adjacent sequences: A164617 A164618 A164619 * A164621 A164622 A164623

Keyword

nonn,easy

Author

Vladimir Joseph Stephan Orlovsky, Aug 17 2009

Extensions

Comments turned into examples by R. J. Mathar, Sep 17 2009

Status

approved