1,2

Table of n, a(n) for n=1..49.

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

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

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

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

Sequence in context: A140509 A314580 A314581 * A235033 A327593 A282757

Adjacent sequences: A272899 A272900 A272901 * A272903 A272904 A272905

nonn,easy

Carlos Valencia Alonso, May 09 2016

approved