A199718 Numbers k such that 6*k-5 is composite, but 6*k-1 is prime.

5, 9, 10, 15, 23, 25, 29, 30, 32, 40, 42, 43, 44, 45, 49, 58, 60, 65, 70, 72, 75, 80, 85, 87, 93, 94, 95, 98, 99, 100, 107, 109, 110, 114, 117, 120, 133, 135, 137, 140, 155, 158, 159, 163, 164, 170, 172, 175, 177, 184, 185, 192, 194, 197, 198, 199, 204, 205

Offset: 1

Author

Eleonora Echeverri-Toro, Nov 09 2011

Keywords

• nonn
• easy

Links

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

Crossrefs

Cf. A186243.

Programs

Magma

[ p div 6 +1: n in [4..204] | not IsPrime(p-4) and p mod 6 eq 5 where p is NthPrime(n) ]; // Bruno Berselli, Nov 09 2011

Mathematica

Select[Range[2, 205], ! PrimeQ[6 # - 5] && PrimeQ[6 # - 1] &] (* T. N. Noe, Nov 09 2011 *)