A054786 Earliest sequence with a(a(n)) = 6n.

0, 2, 6, 4, 18, 7, 12, 30, 9, 48, 11, 60, 36, 14, 78, 16, 90, 19, 24, 102, 21, 120, 23, 132, 108, 26, 150, 28, 162, 31, 42, 174, 33, 192, 35, 204, 72, 38, 222, 40, 234, 43, 180, 246, 45, 264, 47, 276, 54, 50, 294, 52, 306, 55, 288, 318, 57, 336, 59, 348, 66, 62, 366, 64

Offset: 0

Author

Henry Bottomley, Apr 27 2000

Keywords

• nice
• nonn

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, A002517, A002518, A007379.

Programs

Mathematica

a[0] = 0; a[n_] := a[n] = Switch[ Mod[n, 12], 0 | 6, 6*a[n/6], 1 | 3 | 8 | 10, n+1, 2 | 4 | 9 | 11, 6*n-6, 5, n+2, 7, 6*n-12]; Table[a[n], {n, 0, 63}] (* Jean-François Alcover, Dec 20 2011, after formula *)

Formula

a(12n)=6*a(2n), a(12n+1)=12n+2, a(12n+2)=72n+6, a(12n+3)=12n+4, a(12n+4)=72n+18, a(12n+5)=12n+7, a(12n+6)=6*a(2n+1), a(12n+7)=72n+30, a(12n+8)=12n+9, a(12n+9)=72n+48, a(12n+10)=12n+11, a(12n+11)=72n+60.

Extensions

Typo in formula corrected by Reinhard Zumkeller, Jul 23 2010