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 A245339 #17 Aug 04 2025 02:17:26 %S A245339 0,1,2,3,4,5,6,7,8,9,9,10,11,12,13,14,15,16,17,18,17,18,19,20,21,22, %T A245339 23,24,25,26,24,25,26,27,28,29,30,31,32,33,30,31,32,33,34,35,36,37,38, %U A245339 39,35,36,37,38,39,40,41,42,43,44,39,40,41,42,43,44,45,46 %N A245339 Sum of digits of n written in fractional base 10/9. %C A245339 The base 10/9 expansion is unique and thus the sum of digits function is well-defined. %H A245339 Amiram Eldar, <a href="/A245339/b245339.txt">Table of n, a(n) for n = 0..10000</a> %H A245339 <a href="/index/Ba#base_fractional">Index entries for sequences related to fractional bases</a>. %F A245339 a(n) = A007953(A024664(n)). %e A245339 In base 10/9 the number 14 is represented by 94 and so a(14) = 9 + 4 = 13. %t A245339 a[n_] := a[n] = If[n == 0, 0, a[9 * Floor[n/10]] + Mod[n, 10]]; Array[a, 100, 0] (* _Amiram Eldar_, Aug 04 2025 *) %o A245339 (Sage) # uses [basepqsum from A245355] %o A245339 [basepqsum(10,9,w) for w in [0..200]] %o A245339 (PARI) a(n) = if(n == 0, 0, a(n\10 * 9) + n % 10); \\ _Amiram Eldar_, Aug 04 2025 %Y A245339 Cf. A000120, A007953, A024664, A244040. %K A245339 nonn,base,easy %O A245339 0,3 %A A245339 _Hailey R. Olafson_, Jul 18 2014