A168447 Primes p such that floor(p/6) is also prime.

13, 17, 19, 23, 31, 43, 47, 67, 71, 79, 83, 103, 107, 139, 179, 191, 223, 227, 251, 263, 283, 359, 367, 431, 439, 443, 479, 499, 503, 587, 607, 619, 643, 647, 659, 683, 787, 823, 827, 839, 907, 911, 947, 983, 1039, 1087, 1091, 1151, 1163, 1187, 1367, 1399

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Nov 25 2009

Keywords

• nonn
• easy

Links

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

Crossrefs

Cf. A075519, A168446.

Programs

Magma

[p: p in PrimesUpTo(1400) | IsPrime(Floor(p/6))]; // Vincenzo Librandi, Apr 16 2013

Mathematica

Select[Prime[Range[6! ]],PrimeQ[Floor[ #/6]]&]

PARI

is(n)=isprime(n) && isprime(n\6) \\ Charles R Greathouse IV, Feb 23 2017

Formula

a(n) >> n log^2 n. - Charles R Greathouse IV, Feb 23 2017

Extensions

Definition corrected by R. J. Mathar, Dec 06 2009