A371268 If the ternary expansion of n starts with a 1, replace 1's by 2's, 2's by 0's, 0's by 1's, if it starts with a 2, replace 2's by 1's, 1's by 0's, 0's by 2's.

0, 2, 1, 7, 8, 6, 5, 3, 4, 22, 23, 21, 25, 26, 24, 19, 20, 18, 17, 15, 16, 11, 9, 10, 14, 12, 13, 67, 68, 66, 70, 71, 69, 64, 65, 63, 76, 77, 75, 79, 80, 78, 73, 74, 72, 58, 59, 57, 61, 62, 60, 55, 56, 54, 53, 51, 52, 47, 45, 46, 50, 48, 49, 35, 33, 34, 29, 27

Offset: 0

Author

Rémy Sigrist, Mar 16 2024

Keywords

• nonn
• base
• easy

Comments

This sequence is a self-inverse permutation of the nonnegative integers.

Examples

			The first terms, in decimal and in base 3, are:
  n   a(n)  ter(n)  ter(a(n))
  --  ----  ------  ---------
   0     0       0          0
   1     2       1          2
   2     1       2          1
   3     7      10         21
   4     8      11         22
   5     6      12         20
   6     5      20         12
   7     3      21         10
   8     4      22         11
   9    22     100        211
  10    23     101        212
  11    21     102        210
  12    25     110        221
  13    26     111        222
  14    24     112        220
  15    19     120        201
		

Links

• Rémy Sigrist, Table of n, a(n) for n = 0..6560
• Index entries for sequences that are permutations of the natural numbers

Crossrefs

See A004488 and A361945 for similar sequences.

Cf. A338246, A371256.

Programs

PARI

a(n) = { my (d = digits(n, 3)); if (#d, d = if (d[1]==1, apply(v -> [1, 2, 0][1+v], d), apply(v -> [2, 0, 1][1+v], d));); fromdigits(d, 3); }

Formula

A371256(a(n)) = A371256(n).