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 A089293 #13 Aug 04 2021 03:15:22 %S A089293 0,1,1,2,2,3,1,2,2,3,3,4,1,2,2,3,3,4,2,3,3,4,4,5,2,3,3,4,4,5,3,4,4,5, %T A089293 5,6,1,2,2,3,3,4,2,3,3,4,4,5,2,3,3,4,4,5,3,4,4,5,5,6,3,4,4,5,5,6,4,5, %U A089293 5,6,6,7,1,2,2,3,3,4,2,3,3,4,4,5,2,3,3,4,4,5,3,4,4,5,5,6,3,4,4,5,5,6,4,5,5 %N A089293 Sum of digits in the mixed-base enumeration system n=...d(4)d(3)d(2)d(1), where the digits satisfy 0<=d(i)<=1 if i is odd, 0<=d(i)<=2 if i is even. %C A089293 Counting 0,1,2,3,... (base 10) in this mixed-base system proceeds as follows: 0,1,10,11,20,21,100,101,110,111,120,121,1000,.. = A109827. %F A089293 a(n)=a(n-1)+1 if n=1, 3, 5 mod 6; a(n)=a(n-1) if n=2, 4 mod 5; a(n)=a(n/6) if n=0 mod 6. %e A089293 11(base 10) = 121(mixed-base), so a(11)=4. %o A089293 (PARI) a(n) = vecsum(digits(n,6)\/2); \\ _Kevin Ryde_, Aug 03 2021 %Y A089293 Cf. A109827 (mixed-base). %Y A089293 Sums of digits in other bases: A000120 (binary), A053735 (ternary), A053827 (base 6). %K A089293 nonn,base,easy,less %O A089293 0,4 %A A089293 _John W. Layman_, Jan 15 2004