This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A328169 #5 Oct 13 2019 11:20:59
%S A328169 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,
%T A328169 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,
%U A328169 1,1,20,2,1,1,21,1,22,1,1,1,1,1,23,2,3,2
%N A328169 GCD of the prime indices of n, all plus 1.
%C A328169 Zeros are ignored when computing GCD, and the empty set has GCD 0.
%C A328169 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.
%F A328169 a(n) = A289508(A003961(n)).
%e A328169 85 has prime indices {3,7}, so a(85) = GCD(4,8) = 4.
%t A328169 Table[GCD@@(PrimePi/@First/@If[n==1,{},FactorInteger[n]]+1),{n,100}]
%Y A328169 Positions of 0's and 1's are A318981.
%Y A328169 Positions of records (first appearances) appear to be A116974.
%Y A328169 The GCD of the prime indices of n, all minus 1, is A328167(n).
%Y A328169 The LCM of the prime indices of n, all plus 1, is A328219(n).
%Y A328169 Partitions whose parts plus 1 are relatively prime are A318980.
%Y A328169 Cf. A000837, A056239, A112798, A258409, A289508, A289509, A290103, A328168.
%K A328169 nonn
%O A328169 1,2
%A A328169 _Gus Wiseman_, Oct 09 2019