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A023511
Least odd prime divisor of prime(n) + 1, or 1 if prime(n) + 1 is a power of 2.
0
3, 1, 3, 1, 3, 7, 3, 5, 3, 3, 1, 19, 3, 11, 3, 3, 3, 31, 17, 3, 37, 5, 3, 3, 7, 3, 13, 3, 5, 3, 1, 3, 3, 5, 3, 19, 79, 41, 3, 3, 3, 7, 3, 97, 3, 5, 53, 7, 3, 5, 3, 3, 11, 3, 3, 3, 3, 17, 139, 3, 71, 3, 7, 3, 157, 3, 83, 13, 3, 5, 3, 3, 23, 11, 5, 3, 3, 199, 3, 5, 3, 211, 3, 7, 5, 3, 3
OFFSET
1,1
COMMENTS
Note that a(n) = 1 for n= 2, 4, 11, 31, 1028, ... (A059305). - Michel Marcus, Oct 01 2013
FORMULA
a(n) = A078701(A008864(n)). - Michel Marcus, Jun 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
Sequence in context: A046933 A185091 A332031 * A035628 A187562 A370719
KEYWORD
nonn
STATUS
approved