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 A245349 #18 Jul 31 2025 03:51:36 %S A245349 0,1,2,3,4,5,6,4,5,6,7,8,9,10,5,6,7,8,9,10,11,9,10,11,12,13,14,15,7,8, %T A245349 9,10,11,12,13,11,12,13,14,15,16,17,12,13,14,15,16,17,18,7,8,9,10,11, %U A245349 12,13,11,12,13,14,15,16,17,12,13,14,15,16,17 %N A245349 Sum of digits of n written in fractional base 7/4. %C A245349 The base 7/4 expansion is unique, and thus the sum of digits function is well-defined. %H A245349 Amiram Eldar, <a href="/A245349/b245349.txt">Table of n, a(n) for n = 0..10000</a> %H A245349 <a href="/index/Ba#base_fractional">Index entries for sequences related to fractional bases</a>. %F A245349 a(n) = A007953(A024641(n)). - _Amiram Eldar_, Jul 31 2025 %e A245349 In base 7/4 the number 7 is represented by 40 and so a(7) = 4 + 0 = 4. %t A245349 a[n_] := a[n] = If[n == 0, 0, a[4 * Floor[n/7]] + Mod[n, 7]]; Array[a, 100, 0] (* _Amiram Eldar_, Jul 31 2025 *) %o A245349 (Sage) # uses [basepqsum from A245355] %o A245349 [basepqsum(7,4,y) for y in [0..200]] %o A245349 (PARI) a(n) = if(n == 0, 0, a(n\7 * 4) + n % 7); \\ _Amiram Eldar_, Jul 31 2025 %Y A245349 Cf. A024641, A053828, A007953. %K A245349 nonn,base,easy %O A245349 0,3 %A A245349 _James Van Alstine_, Jul 18 2014