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