cp's OEIS Frontend

A328167 GCD of the prime indices of n, all minus 1.

%I A328167 #7 Oct 13 2019 11:19:31
%S A328167 0,0,1,0,2,1,3,0,1,2,4,1,5,3,1,0,6,1,7,2,1,4,8,1,2,5,1,3,9,1,10,0,1,6,
%T A328167 1,1,11,7,1,2,12,1,13,4,1,8,14,1,3,2,1,5,15,1,2,3,1,9,16,1,17,10,1,0,
%U A328167 1,1,18,6,1,1,19,1,20,11,1,7,1,1,21,2,1,12
%N A328167 GCD of the prime indices of n, all minus 1.
%C A328167 Zeros are ignored when computing GCD, and the empty set has GCD 0.
%C A328167 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.
%e A328167 85 has prime indices {3,7}, so a(85) = GCD(2,6) = 2.
%t A328167 Table[GCD@@(PrimePi/@First/@If[n==1,{},FactorInteger[n]]-1),{n,100}]
%Y A328167 Positions of 0's are A000079.
%Y A328167 Positions of 1's are A328168.
%Y A328167 Positions of records (first appearances) are A006005.
%Y A328167 The GCD of the prime indices of n is A289508(n).
%Y A328167 The GCD of the prime indices of n, all plus 1, is A328169(n).
%Y A328167 Looking at divisors instead of prime indices gives A258409.
%Y A328167 Partitions whose parts minus 1 are relatively prime are A328170.
%Y A328167 Cf. A000837, A001222, A007359, A056239, A112798, A289509, A318978, A318981, A328163, A328164.
%K A328167 nonn
%O A328167 1,5
%A A328167 _Gus Wiseman_, Oct 08 2019