A181099 Exchange rightmost two ternary digits of n > 1; a(0)=0, a(1)=3.

0, 3, 6, 1, 4, 7, 2, 5, 8, 9, 12, 15, 10, 13, 16, 11, 14, 17, 18, 21, 24, 19, 22, 25, 20, 23, 26, 27, 30, 33, 28, 31, 34, 29, 32, 35, 36, 39, 42, 37, 40, 43, 38, 41, 44, 45, 48, 51, 46, 49, 52, 47, 50, 53, 54, 57, 60, 55, 58, 61, 56, 59, 62, 63, 66, 69, 64, 67, 70, 65, 68, 71, 72

Offset

0,2

Comments

Self-inverse permutation of natural numbers: a(a(n)) = n.

Links

Table of n, a(n) for n=0..72.

Index entries for sequences that are permutations of the natural numbers.

Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,0,0,0,1,-1).

Formula

From R. J. Mathar, Oct 12 2010: (Start)

a(n) = a(n-1) + a(n-9) - a(n-10) = 9 *floor(n/9) + 3*(n mod 3) + (floor(n/3) mod 3).

G.f.: x*(3 + 3*x - 5*x^2 + 3*x^3 + 3*x^4 - 5*x^5 + 3*x^6 + 3*x^7 + x^8) / ( (1+x+x^2)*(x^6+x^3+1)*(x-1)^2 ). (End)

Example

a(10) = a(101_3) = 110_3 = 12.
a(20) = a(202_3) = 220_3 = 24.
a(30) = a(1010_3) = 1001_3 = 28.

Crossrefs

Cf. A007089, A080412.

Sequence in context: A195699 A199795 A200358 * A163327 A338460 A175032

Adjacent sequences: A181096 A181097 A181098 * A181100 A181101 A181102

Keyword

base,easy,nonn,changed

Author

Jonathan Vos Post, Oct 03 2010

Extensions

Corrected and extended by D. S. McNeil, Oct 06 2010

Status

approved