A086410 Smallest prime factor of 3-smooth numbers, with a(1)=1.

1, 2, 3, 2, 2, 2, 3, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2

Offset: 1

Author

Reinhard Zumkeller, Jul 18 2003

Keywords

• nonn
• nice

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003586, A006899, A020639, A033845, A086411.

Programs

Mathematica

Reap[For[n = 1, n <= 2*10^5, n++, If[EulerPhi[6*n] == 2*n, Sow[ FactorInteger[n][[1, 1]]]]]][[2, 1]] (* Jean-François Alcover, Sep 02 2016 *)

Formula

a(n) = A020639(A003586(n));

a(n) <= A086411(n) <= 3.

a(A033845(n)) = A086411(A033845(n))-1; a(A006899(n)) = A086411(A006899(n)). - Reinhard Zumkeller, Sep 25 2008