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 A245353 #13 Aug 02 2025 06:27:01 %S A245353 0,1,2,3,4,5,6,7,8,7,8,9,10,11,12,13,14,15,12,13,14,15,16,17,18,19,20, %T A245353 15,16,17,18,19,20,21,22,23,16,17,18,19,20,21,22,23,24,23,24,25,26,27, %U A245353 28,29,30,31,22,23,24,25,26,27,28,29,30,27,28,29,30,31 %N A245353 Sum of digits of n written in fractional base 9/7. %C A245353 The base 9/7 expansion is unique and thus the sum of digits function is well-defined. %H A245353 Amiram Eldar, <a href="/A245353/b245353.txt">Table of n, a(n) for n = 0..10000</a> %H A245353 <a href="/index/Ba#base_fractional">Index entries for sequences related to fractional bases</a>. %F A245353 a(n) = A007953(A024655(n)). %e A245353 In base 9/7 the number 14 is represented by 75 and so a(14) = 7 + 5 = 12. %t A245353 a[n_] := a[n] = If[n == 0, 0, a[7 * Floor[n/9]] + Mod[n, 9]]; Array[a, 100, 0] (* _Amiram Eldar_, Aug 02 2025 *) %o A245353 (Sage) # uses [basepqsum from A245355] %o A245353 [basepqsum(9,7,w) for w in [0..200]] %o A245353 (PARI) a(n) = if(n == 0, 0, a(n\9 * 7) + n % 9); \\ _Amiram Eldar_, Aug 02 2025 %Y A245353 Cf. A000120, A007953, A024655, A053830, A244040. %K A245353 nonn,base,easy %O A245353 0,3 %A A245353 _Hailey R. Olafson_, Jul 18 2014