A023578 Least odd prime divisor of prime(n)+3, or 1 if prime(n)+3 is a power of 2.

5, 3, 1, 5, 7, 1, 5, 11, 13, 1, 17, 5, 11, 23, 5, 7, 31, 1, 5, 37, 19, 41, 43, 23, 5, 13, 53, 5, 7, 29, 5, 67, 5, 71, 19, 7, 5, 83, 5, 11, 7, 23, 97, 7, 5, 101, 107, 113, 5, 29, 59, 11, 61, 127, 5, 7, 17, 137, 5, 71, 11, 37, 5, 157, 79, 5, 167, 5, 5, 11, 89, 181, 5, 47, 191

Offset

1,1

Links

Table of n, a(n) for n=1..75.

Formula

a(n) = A078701(A113935(n)). - Michel Marcus, Aug 05 2021

Prog

(PARI) a(n) = my(p = prime(n)+3, v = p/(2^valuation(p, 2))) ; if (v == 1, 1, factor(v)[1, 1]); \\ Michel Marcus, Aug 05 2021
(Python)
from sympy import factorint, prime
def A023578(n): return min((p for p in factorint(prime(n)+3) if p > 2), default=1) # Chai Wah Wu, Feb 03 2022

Crossrefs

Cf. A023505, A078701, A113935.

Sequence in context: A092235 A130794 A242908 * A111487 A011505 A373672

Adjacent sequences: A023575 A023576 A023577 * A023579 A023580 A023581

Keyword

nonn

Author

Clark Kimberling

Status

approved