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 A245351 #14 Aug 04 2025 02:17:40 %S A245351 0,1,2,3,4,5,6,7,8,9,7,8,9,10,11,12,13,14,15,16,11,12,13,14,15,16,17, %T A245351 18,19,20,12,13,14,15,16,17,18,19,20,21,19,20,21,22,23,24,25,26,27,28, %U A245351 17,18,19,20,21,22,23,24,25,26,21,22,23,24,25,26,27,28 %N A245351 Sum of digits of n written in fractional base 10/7. %C A245351 The base 10/7 expansion is unique and thus the sum of digits function is well-defined. %H A245351 Amiram Eldar, <a href="/A245351/b245351.txt">Table of n, a(n) for n = 0..10000</a> %H A245351 <a href="/index/Ba#base_fractional">Index entries for sequences related to fractional bases</a>. %F A245351 a(n) = A007953(A024662(n)). %e A245351 In base 10/7 the number 14 is represented by 74 and so a(14) = 7 + 4 = 11. %t A245351 a[n_] := a[n] = If[n == 0, 0, a[7 * Floor[n/10]] + Mod[n, 10]]; Array[a, 100, 0] (* _Amiram Eldar_, Aug 04 2025 *) %o A245351 (Sage) # uses [basepqsum from A245355] %o A245351 [basepqsum(10,7,w) for w in [0..200]] %o A245351 (PARI) a(n) = if(n == 0, 0, a(n\10 * 7) + n % 10); \\ _Amiram Eldar_, Aug 04 2025 %Y A245351 Cf. A000120, A007953, A024662, A244040. %K A245351 nonn,base,easy %O A245351 0,3 %A A245351 _Hailey R. Olafson_, Jul 18 2014