A217122 a(n) = (number of 1's in binary expansion of n)th positive number not among the previous terms.

1, 2, 4, 3, 6, 7, 9, 5, 10, 11, 13, 12, 15, 16, 18, 8, 17, 19, 21, 20, 23, 24, 26, 22, 27, 28, 30, 29, 32, 33, 35, 14, 31, 34, 37, 36, 39, 40, 42, 38, 43, 44, 46, 45, 48, 49, 51, 41, 50, 52, 54, 53, 56, 57, 59, 55, 60, 61, 63, 62, 65, 66, 68, 25, 58, 64, 69, 67, 71, 72, 74, 70, 75, 76, 78, 77, 80, 81, 83, 73, 82, 84, 86, 85, 88, 89, 91, 87, 92

Offset: 1

Author

Paul Tek, Mar 16 2013

Keywords

• nonn
• base

Comments

This is a permutation of the positive numbers.

Examples

			3 has 2 1's in its binary expansion, and the 2nd positive number not among the previous terms is 4; hence a(3)=4
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Index entries for sequences that are permutations of the natural numbers

Crossrefs

Cf. A000120: number of 1's in binary expansion of n.

Cf. A225589 (inverse), A075311.

Programs

Haskell

import Data.List (delete)
a217122 n = a217122_list !! (n-1)
a217122_list = f 1 [0..] where
   f x zs = y : f (x + 1) (delete y zs) where
     y = zs !! a000120 x
-- Reinhard Zumkeller, May 11 2013