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
Keywords
Programs
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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
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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