A258568 Smallest prime factors of 3-full numbers.

1, 2, 2, 3, 2, 2, 3, 5, 2, 2, 3, 2, 7, 2, 2, 5, 2, 3, 2, 2, 2, 2, 11, 2, 2, 2, 2, 3, 13, 7, 2, 2, 5, 3, 2, 2, 2, 2, 17, 2, 2, 2, 2, 3, 19, 2, 2, 2, 2, 3, 2, 3, 2, 2, 2, 2, 23, 2, 11, 2, 5, 2, 2, 7, 3, 2, 2, 2, 3, 2, 2, 2, 2, 2, 29, 2, 2, 2, 3, 13, 31, 3, 2, 2

Offset: 1

Author

Reinhard Zumkeller, Jun 06 2015

Keywords

• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 (corrected by Amiram Eldar)

Crossrefs

Cf. A036966, A020639, A258600, A258567, A258569, A258570, A258571.

Programs

Haskell

a258568 = a020639 . a036966

Mathematica

Table[If[Min[(f = FactorInteger[n])[[;; , 2]]] > 2 || n == 1, f[[1, 1]], Nothing], {n, 1, 30000}] (* Amiram Eldar, Feb 07 2023 *)

Formula

a(n) = A020639(A036966(n)).

a(A258600(n)) = A000040(n) and a(m) != A000040(n) for m < A258600(n).

Extensions

Missing term a(78) inserted by Amiram Eldar, Feb 07 2023