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 A245350 #19 Aug 02 2025 06:26:55 %S A245350 0,1,2,3,4,5,6,7,8,4,5,6,7,8,9,10,11,12,8,9,10,11,12,13,14,15,16,7,8, %T A245350 9,10,11,12,13,14,15,11,12,13,14,15,16,17,18,19,10,11,12,13,14,15,16, %U A245350 17,18,14,15,16,17,18,19,20,21,22,8,9,10,11,12,13,14,15 %N A245350 Sum of digits of n written in fractional base 9/4. %C A245350 The base 9/4 expansion is unique and thus the sum of digits function is well-defined. %H A245350 Amiram Eldar, <a href="/A245350/b245350.txt">Table of n, a(n) for n = 0..10000</a> %H A245350 <a href="/index/Ba#base_fractional">Index entries for sequences related to fractional bases</a>. %F A245350 a(n) = A007953(A024652(n)). %e A245350 In base 9/4 the number 16 is represented by 47 and so a(16) = 4 + 7 = 11. %t A245350 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 A245350 (Sage) # uses [basepqsum from A245355] %o A245350 [basepqsum(9,4,i) for i in [0..100]] %o A245350 (PARI) a(n) = if(n == 0, 0, a(n\9 * 4) + n % 9); \\ _Amiram Eldar_, Aug 02 2025 %Y A245350 Cf. A000120, A007953, A024652, A053830, A244040. %K A245350 nonn,base,easy %O A245350 0,3 %A A245350 _Tom Edgar_, Jul 18 2014