A024657 n written in fractional base 10/2.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 220, 221, 222, 223, 224, 225, 226, 227

Offset: 0

Author

David W. Wilson

Keywords

• nonn
• base
• easy

Comments

To represent a number in base b, if a digit exceeds b-1, subtract b and carry 1. In fractional base a/b, subtract a and carry b.

Also numbers which are written the same in base 20/2 as in base 10. The sequence consists of numbers which have digits in {0,2,4,6,8} except that the unit digit can be any from {0,1,2,3,4,5,6,7,8,9} - Henry Bottomley, Nov 17 2000

Links

• Amiram Eldar, Table of n, a(n) for n = 0..10000
• Index entries for sequences related to fractional bases.

Crossrefs

Cf. A007091, A058185, A058186, A102491, A118761.

Programs

Mathematica

a[n_] := a[n] = If[n == 0, 0, 10 * a[2 * Floor[n/10]] + Mod[n, 10]]; Array[a, 50, 0] (* Amiram Eldar, Aug 02 2025 *)

PARI

a(n) = if(n == 0, 0, 10 * a(n\10 * 2) + n % 10); \\ Amiram Eldar, Aug 02 2025

Formula

a(n) = A118761(n+1) for n < 50. - Reinhard Zumkeller, May 01 2006