A272902 Numbers k such that 6*k - 5 is not prime.

1, 5, 9, 10, 15, 16, 20, 21, 23, 25, 29, 30, 32, 35, 37, 40, 42, 43, 44, 45, 49, 50, 51, 54, 55, 58, 60, 61, 65, 66, 68, 70, 72, 75, 76, 79, 80, 81, 83, 85, 86, 87, 89, 90, 93, 94, 95, 98, 99, 100, 105, 107, 109, 110, 112, 114, 115, 117, 118, 120, 121, 125, 128, 130, 131

Offset

1,2

Links

Andrew Howroyd, Table of n, a(n) for n = 1..10000

Formula

a(n) ~ n. - Charles R Greathouse IV, May 09 2016

Example

a(2) = 5 because 6 * 5 - 5 = 25 which is composite.

Mathematica

Select[Range[100], Not[PrimeQ[6# - 5]] &] (* Alonso del Arte, May 09 2016 *)

Prog

(PARI) is(n)=!isprime(6*n-5) \\ Charles R Greathouse IV, May 09 2016

Crossrefs

Sequence in context: A140509 A314580 A314581 * A235033 A327593 A282757

Adjacent sequences: A272899 A272900 A272901 * A272903 A272904 A272905

Keyword

nonn,easy

Author

Carlos Valencia Alonso, May 09 2016

Extensions

a(50) onward from Andrew Howroyd, Oct 30 2025

Status

approved