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A328169
GCD of the prime indices of n, all plus 1.
9
0, 2, 3, 2, 4, 1, 5, 2, 3, 2, 6, 1, 7, 1, 1, 2, 8, 1, 9, 2, 1, 2, 10, 1, 4, 1, 3, 1, 11, 1, 12, 2, 3, 2, 1, 1, 13, 1, 1, 2, 14, 1, 15, 2, 1, 2, 16, 1, 5, 2, 1, 1, 17, 1, 2, 1, 3, 1, 18, 1, 19, 2, 1, 2, 1, 1, 20, 2, 1, 1, 21, 1, 22, 1, 1, 1, 1, 1, 23, 2, 3, 2
OFFSET
1,2
COMMENTS
Zeros are ignored when computing GCD, and the empty set has GCD 0.
A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
FORMULA
a(n) = A289508(A003961(n)).
EXAMPLE
85 has prime indices {3,7}, so a(85) = GCD(4,8) = 4.
MATHEMATICA
Table[GCD@@(PrimePi/@First/@If[n==1, {}, FactorInteger[n]]+1), {n, 100}]
CROSSREFS
Positions of 0's and 1's are A318981.
Positions of records (first appearances) appear to be A116974.
The GCD of the prime indices of n, all minus 1, is A328167(n).
The LCM of the prime indices of n, all plus 1, is A328219(n).
Partitions whose parts plus 1 are relatively prime are A318980.
Sequence in context: A079528 A143422 A071438 * A353951 A030011 A286000
KEYWORD
nonn
AUTHOR
Gus Wiseman, Oct 09 2019
STATUS
approved