%I #7 Mar 30 2012 18:38:56
%S 0,1,9,901,901009,901009000901,901009000901000000901009,
%T 901009000901000000901009000000000000901009000901,
%U 901009000901000000901009000000000000901009000901000000000000000000000000901009000901000000901009
%N a(1)=0 a(2)=1 a(n)=concatenate(a(n-1)a(n-2)...a(1))-a(n-1).
%e a(5)=concatenate(a(4)a(3)a(2)a(1))-a(4)=901910-901=901009
%K easy,nonn,base
%O 1,3
%A _Benoit Cloitre_, Apr 03 2002