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%I #13 Aug 04 2021 03:15:22
%S 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 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 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 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 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 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 11(base 10) = 121(mixed-base), so a(11)=4.
%o (PARI) a(n) = vecsum(digits(n,6)\/2); \\ _Kevin Ryde_, Aug 03 2021
%Y Cf. A109827 (mixed-base).
%Y Sums of digits in other bases: A000120 (binary), A053735 (ternary), A053827 (base 6).
%K nonn,base,easy,less
%O 0,4
%A _John W. Layman_, Jan 15 2004
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