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 A245354 #14 Aug 02 2025 06:27:04 %S A245354 0,1,2,3,4,5,6,7,8,5,6,7,8,9,10,11,12,13,6,7,8,9,10,11,12,13,14,11,12, %T A245354 13,14,15,16,17,18,19,8,9,10,11,12,13,14,15,16,13,14,15,16,17,18,19, %U A245354 20,21,14,15,16,17,18,19,20,21,22,19,20,21,22,23 %N A245354 Sum of digits of n in fractional base 9/5. %C A245354 The base 9/5 expansion is unique, and thus the sum of digits function is well-defined. %H A245354 Amiram Eldar, <a href="/A245354/b245354.txt">Table of n, a(n) for n = 0..10000</a> %H A245354 <a href="/index/Ba#base_fractional">Index entries for sequences related to fractional bases</a>. %F A245354 a(n) = A007953(A024653(n)). - _Amiram Eldar_, Aug 02 2025 %e A245354 In base 9/5 the number 11 is represented by 52 and so a(11) = 5 + 2 = 7. %t A245354 a[n_] := a[n] = If[n == 0, 0, a[4 * Floor[n/9]] + Mod[n, 9]]; Array[a, 100, 0] (* _Amiram Eldar_, Aug 02 2025 *) %o A245354 (Sage) # uses [basepqsum from A245355] %o A245354 [basepqsum(9,5,y) for y in [0..200]] %o A245354 (PARI) a(n) = if(n == 0, 0, a(n\9 * 4) + n % 9); \\ _Amiram Eldar_, Aug 02 2025 %Y A245354 Cf. A007953, A024653, A053830. %K A245354 nonn,base,easy %O A245354 0,3 %A A245354 _James Van Alstine_, Jul 18 2014