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a(n)=(# 1's)-(# 2's) in first n terms of A031235.
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%I #6 Aug 02 2016 10:25:22

%S 1,0,0,0,0,1,2,3,2,3,3,4,4,5,5,4,5,4,3,2,2,1,1,0,0,0,1,1,0,0,0,0,0,0,

%T 0,0,1,1,0,0,0,0,0,0,0,0,1,2,2,3,2,2,3,3,3,4,4,4,5,5,6,7,8,9,10,9,10,

%U 11,11,12,13,13,14,15,15,14,15,16,15,16,15,14

%N a(n)=(# 1's)-(# 2's) in first n terms of A031235.

%t Accumulate[Which[#==1,1,#==2,-1,True,0]&/@(Reverse[IntegerDigits[ #,5]]&/@ Range[ 0,40]//Flatten)] (* _Harvey P. Dale_, Aug 02 2016 *)

%K nonn

%O 1,7

%A _Clark Kimberling_