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 A245335 #31 Jul 31 2025 03:49:19 %S A245335 0,1,2,3,4,4,5,6,7,8,7,8,9,10,11,9,10,11,12,13,10,11,12,13,14,10,11, %T A245335 12,13,14,14,15,16,17,18,13,14,15,16,17,16,17,18,19,20,14,15,16,17,18, %U A245335 16,17,18,19,20,20,21,22,23,24,17,18,19,20,21,18,19,20,21 %N A245335 Sum of digits of n in fractional base 5/4. %C A245335 The base 5/4 expansion is unique and thus the sum of digits function is well-defined. %H A245335 Amiram Eldar, <a href="/A245335/b245335.txt">Table of n, a(n) for n = 0..10000</a> %H A245335 <a href="/index/Ba#base_fractional">Index entries for sequences related to fractional bases</a>. %F A245335 a(n) = A007953(A024634(n)). - _Kevin Ryde_, Aug 11 2023 %e A245335 In base 5/4 the number 7 is represented by 42 and so a(7) = 4+2 = 6. %t A245335 a[n_] := a[n] = If[n == 0, 0, a[4 * Floor[n/5]] + Mod[n, 5]]; Array[a, 100, 0] (* _Amiram Eldar_, Jul 31 2025 *) %o A245335 (Sage) # uses [basepqsum from A245355] %o A245335 [basepqsum(5,4,y) for y in [0..200]] %o A245335 (PARI) a(n) = my(ret=0,r); while(n, [n,r]=divrem(n,5); ret+=r; n<<=2); ret; \\ _Kevin Ryde_, Aug 11 2023 %Y A245335 Cf. A024634, A007953, A053824. %K A245335 nonn,base,easy %O A245335 0,3 %A A245335 _James Van Alstine_, Jul 18 2014