A377513 a(n) = number of iterations of x -> 2 x - 5 to reach a nonprime, starting with prime(n+4).

8, 1, 7, 1, 2, 6, 1, 1, 1, 1, 3, 5, 2, 1, 1, 3, 1, 1, 1, 2, 1, 4, 1, 1, 1, 1, 1, 4, 2, 1, 2, 1, 1, 1, 1, 1, 3, 1, 1, 1, 3, 1, 1, 1, 2, 1, 2, 1, 1, 1, 3, 2, 1, 1, 1, 7, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 2, 1, 2, 1, 1, 1, 4, 1, 1, 2, 1, 1, 1, 1

Offset: 1

Author

Clark Kimberling, Nov 05 2024

Keywords

• nonn

Comments

See A377120 for a guide to related sequences.

Examples

			prime(5) = 11 -> 17 -> 29 -> 53 -> 101 -> 197 -> 389 -> 773 -> 1541 = 23*67,
so a(1) = 8.
		

Crossrefs

Cf. A377120, A377510, A377511, A377512, A377514.

Programs

Mathematica

Table[p = Prime[n + 4]; c = 1; While[p = 2*p - 5; PrimeQ[p], c++]; c, {n, 200}]