A187921 Positions k of addition steps in Recamán's sequence where A005132(k-1)<=k.

1, 2, 3, 5, 11, 13, 15, 17, 24, 26, 28, 30, 32, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 112, 130, 132, 137, 139, 141, 143, 145, 147, 149, 151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171, 197, 199, 201, 203, 205, 207, 209, 211, 213, 215, 217, 219, 221, 223, 248, 250

Offset: 1

Author

Reinhard Zumkeller, Mar 17 2011

Keywords

• nonn

Examples

			a(10)=26: A005132(26-1) = 17 and 17-26<0, hence A005132(26) = 17+26 = 43.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to Recamán's sequence

Crossrefs

Subsequence of A057165;

A005132(a(n)-1) <= a(n); A005132(a(n)) = A005132(a(n)-1) + a(n);

see A187922 for the other positions of addition steps in A005132.

Programs

Haskell

import Data.Set (Set, singleton, member, insert)
a187921 n = a187921_list !! (n-1)
a187921_list = r (singleton 0) 1 0 where
   r :: Set Integer -> Integer -> Integer -> [Integer]
   r s n x | x <= n           = n : r (insert (x+n) s) (n+1) (x+n)
           | (x-n) `member` s = r (insert (x+n) s) (n+1) (x+n)
           | otherwise        = r (insert (x-n) s) (n+1) (x-n)