This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A024657 #17 Aug 02 2025 06:26:19
%S A024657 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,
%T A024657 46,47,48,49,60,61,62,63,64,65,66,67,68,69,80,81,82,83,84,85,86,87,88,
%U A024657 89,200,201,202,203,204,205,206,207,208,209,220,221,222,223,224,225,226,227
%N A024657 n written in fractional base 10/2.
%C A024657 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.
%C A024657 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
%H A024657 Amiram Eldar, <a href="/A024657/b024657.txt">Table of n, a(n) for n = 0..10000</a>
%H A024657 <a href="/index/Ba#base_fractional">Index entries for sequences related to fractional bases</a>.
%F A024657 a(n) = A118761(n+1) for n < 50. - _Reinhard Zumkeller_, May 01 2006
%t A024657 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 *)
%o A024657 (PARI) a(n) = if(n == 0, 0, 10 * a(n\10 * 2) + n % 10); \\ _Amiram Eldar_, Aug 02 2025
%Y A024657 Cf. A007091, A058185, A058186, A102491, A118761.
%K A024657 nonn,base,easy
%O A024657 0,3
%A A024657 _David W. Wilson_