A377514 a(n) = number of iterations of x -> 2 x - 7 to reach a nonprime, starting with prime(n+4).

1, 3, 1, 2, 1, 1, 1, 3, 1, 3, 1, 1, 1, 1, 2, 1, 3, 2, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 2, 1, 1, 3, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 2, 1, 3, 1, 1, 1, 1, 2, 1, 1, 4, 3, 2, 1, 1, 3, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3

Offset: 1

Author

Clark Kimberling, Nov 05 2024

Keywords

• nonn

Comments

See A377120 for a guide to related sequences.

Examples

			prime(6) = 13 -> 19 -> 31 -> 55 = 5*11, so a(2) = 3.
		

Crossrefs

Cf. A377120, A377510, A377511, A377512, A377513.

Programs

Mathematica

Table[p = Prime[n + 4]; c = 1; While[p = 2*p - 7; PrimeQ[p], c++]; c, {n, 200}]