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a(0) = 0; a(n) = a(n/5)/5 if n = a(n/5) = 0 (mod 5); a(n) = a(n-1)+1 otherwise.
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%I #5 Mar 30 2012 18:35:25

%S 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,1,2,

%T 3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,2,3,4,

%U 5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,3,4,5,6,7,8,9,10

%N a(0) = 0; a(n) = a(n/5)/5 if n = a(n/5) = 0 (mod 5); a(n) = a(n-1)+1 otherwise.

%K nonn

%O 0,3

%A _David W. Wilson_

%E Bounded, conjectured maximum is a(3169) = 49.