A327393 Maximum stable divisor of n.

1, 2, 3, 4, 5, 3, 7, 8, 9, 5, 11, 4, 13, 7, 15, 16, 17, 9, 19, 5, 7, 11, 23, 8, 25, 13, 27, 7, 29, 15, 31, 32, 33, 17, 35, 9, 37, 19, 13, 8, 41, 7, 43, 11, 45, 23, 47, 16, 49, 25, 51, 13, 53, 27, 55, 8, 19, 29, 59, 15, 61, 31, 9, 64, 13, 33, 67, 17, 69, 35, 71

Offset: 1

Author

Gus Wiseman, Sep 15 2019

Keywords

• nonn

Comments

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. A number is stable if its distinct prime indices are pairwise indivisible. Stable numbers are listed in A316476, which is the union of this sequence without 1.

Examples

			The stable divisors of 60 are {1, 2, 3, 4, 5, 15}, so a(60) = 15.
		

Links

• Gus Wiseman, Sequences counting and encoding certain classes of multisets

Crossrefs

See link for additional cross-references.

Cf. A000005, A006530, A302242, A303362.

Programs

Mathematica

stableQ[u_,Q_]:=!Apply[Or,Outer[#1=!=#2&&Q[#1,#2]&,u,u,1],{0,1}];
Table[Max[Select[Divisors[n],stableQ[PrimePi/@First/@FactorInteger[#],Divisible]&]],{n,100}]