A002517 Earliest sequence with a(a(n))=3n.

0, 2, 3, 6, 5, 12, 9, 8, 21, 18, 11, 30, 15, 14, 39, 36, 17, 48, 27, 20, 57, 24, 23, 66, 63, 26, 75, 54, 29, 84, 33, 32, 93, 90, 35, 102, 45, 38, 111, 42, 41, 120, 117, 44, 129, 108, 47, 138, 51, 50, 147, 144, 53, 156, 81, 56, 165, 60, 59, 174, 171, 62, 183, 72, 65, 192

Offset: 0

Author

Colin Mallows

Keywords

• nonn
• nice
• easy

Comments

a(3*n+1) = A016789(n), a(3*n+2) = A017197(n). - Reinhard Zumkeller, Jun 04 2015

Links

• T. D. Noe, Table of n, a(n) for n = 0..1000
• Index entries for sequences of the a(a(n)) = 2n family

Crossrefs

Cf. A002516, A007379, A005843.

Cf. A007494 (sorted), A016789, A017197.

Programs

Haskell

import Data.List (transpose)
a002517 n = a002517_list !! n
a002517_list = 0 : concat
   (transpose [[2, 5 ..], [3, 12 ..], map (* 3) $ tail a002517_list])
-- Reinhard Zumkeller, Jun 04 2015

Mathematica

a[n_] := a[n] = Which[ Mod[n, 3] == 0, 3*a[n/3], Mod[n, 3] == 1, n+1, True, 3*(n-1)]; Table[a[n], {n, 0, 65}] (* Jean-François Alcover, Sep 24 2012 *)

Formula

a(3n)=3*a(n), a(3n+1)=3n+2, a(3n+2)=9n+3

Extensions

Formula and more terms from Henry Bottomley, Apr 27 2000