A059324 Numbers n such that 6n + 5 is composite.

5, 10, 12, 15, 19, 20, 23, 25, 26, 30, 33, 34, 35, 36, 40, 45, 47, 49, 50, 53, 54, 55, 56, 60, 61, 62, 65, 67, 68, 70, 72, 75, 78, 80, 82, 85, 87, 88, 89, 90, 91, 95, 96, 100, 101, 103, 104, 105, 110, 111, 114, 115, 117, 118, 120, 121, 122, 124, 125, 127, 129, 130

Offset: 1

Author

Anton Joha, Jan 26 2001

Keywords

• nonn
• easy

Comments

Conjecture: There exists no pair of primes (p, q > p^2) such that q - p^2 = 6*n - 4 (see A138479). - Philippe LALLOUET (philip.lallouet(AT)orange.fr), Mar 20 2008

Examples

			a(3) = 12 because 6*12 + 5 = 77 is composite.
		

Links

• G. C. Greubel, Table of n, a(n) for n = 1..5000

Crossrefs

Complement of A059325.

Cf. A138479.

Programs

Mathematica

Select[Range[200],!PrimeQ[6#+5]&]  (* Harvey P. Dale, Mar 13 2011 *)

PARI

isok(n) = ! isprime(6*n+5); \\ Michel Marcus, Jan 06 2017

Formula

a(n) = A046953(n-1) - 1.

Extensions

More terms from Henry Bottomley, Jan 29 2001