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

1,2

Links

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

Formula

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

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

Mathematica

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

Prog

(Haskell)
a258568 = a020639 . a036966

Crossrefs

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

Sequence in context: A254618 A268672 A054483 * A108939 A370835 A362972

Adjacent sequences: A258565 A258566 A258567 * A258569 A258570 A258571

Keyword

nonn

Author

Reinhard Zumkeller, Jun 06 2015

Extensions

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

Status

approved