A094510 Smallest number distinct from n, not occurring earlier and having in binary representation exactly as many ones as n.

2, 1, 5, 8, 3, 9, 11, 4, 6, 12, 7, 10, 14, 13, 23, 32, 18, 17, 21, 24, 19, 25, 15, 20, 22, 28, 29, 26, 27, 39, 47, 16, 34, 33, 37, 40, 35, 41, 30, 36, 38, 44, 45, 42, 43, 51, 31, 65, 50, 49, 46, 56, 54, 53, 59, 52, 58, 57, 55, 71, 62, 61, 95, 128, 48, 68, 69, 66, 67, 73, 60

Offset: 1

Author

Reinhard Zumkeller, May 06 2004

Keywords

• nonn

Comments

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

Links

• Paul Tek, Table of n, a(n) for n = 1..10000
• Index entries for sequences that are permutations of the natural numbers
• Index entries for sequences related to binary expansion of n

Crossrefs

Cf. A094511, A007088, A000120.

Programs

Haskell

import Data.List (delete)
a094510 n = a094510_list !! (n-1)
a094510_list = f 1 [1..] where
   f x zs = g zs where
     g (y:ys) = if y /= x && a000120 y == wt
                   then y : f (x + 1) (delete y zs) else g ys
     wt = a000120 x
-- Reinhard Zumkeller, Nov 23 2014