A023505 Least odd prime divisor of prime(n) - 1, or 1 if prime(n) - 1 is a power of 2.

1, 1, 1, 3, 5, 3, 1, 3, 11, 7, 3, 3, 5, 3, 23, 13, 29, 3, 3, 5, 3, 3, 41, 11, 3, 5, 3, 53, 3, 7, 3, 5, 17, 3, 37, 3, 3, 3, 83, 43, 89, 3, 5, 3, 7, 3, 3, 3, 113, 3, 29, 7, 3, 5, 1, 131, 67, 3, 3, 5, 3, 73, 3, 5, 3, 79, 3, 3, 173, 3, 11, 179, 3, 3, 3, 191, 97, 3, 5, 3, 11, 3, 5, 3, 3

Offset

1,4

Comments

Note that a(n)=1 for n= 1,2,3,7,55,6543, ... . - Michel Marcus, Oct 01 2013

Links

Table of n, a(n) for n=1..85.

Formula

a(n) = A078701(A006093(n)). - R. J. Mathar, Feb 06 2019

Prog

(PARI) a(n) = my(p = prime(n) - 1, v = p/(2^valuation(p, 2))) ; if (v == 1, 1, factor(v)[1, 1]); \\ Michel Marcus, Oct 01 2013

Crossrefs

Cf. A006093, A078701.

Sequence in context: A162777 A241014 A173454 * A356489 A196997 A254934

Adjacent sequences: A023502 A023503 A023504 * A023506 A023507 A023508

Keyword

nonn

Author

Clark Kimberling

Status

approved