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 A089601 #9 Feb 17 2015 20:26:26 %S A089601 0,0,1,1,2,10,11,11,12,20,21,101,102,110,111,111,112,120,121,201,202, %T A089601 210,211,1011,1012,1020,1021,1101,1102,1110,1111,1111,1112,1120,1121, %U A089601 1201,1202,1210,1211,2011,2012,2020,2021,2101,2102,2110,2111,10111 %N A089601 Interleaving of A089591 and A089600. %F A089601 To get a(n), drop last digit from either A089591(n) or A089600(n+1). %p A089601 A089591 := proc(n) option remember ; local nhalf ; if n <= 1 then RETURN(n) ; else nhalf := floor(n/2) ; if n mod 2 = 1 then RETURN(10*A089591(nhalf) +1) ; else RETURN(10*(A089591(nhalf-1)+1)) ; fi ; fi ; end: A089600 := proc(n) option remember ; local nhalf ; nhalf := floor(n/2) ; if n <= 1 then RETURN(n) ; else if n mod 2 = 1 then RETURN(10*A089600(nhalf) +1) ; else RETURN(10*A089591(nhalf-1)+2) ; fi ; fi ; end: A089601 := proc(n) if n mod 2 = 0 then A089600(n/2) ; else A089591((n-1)/2) ; fi ; end: seq(A089601(n),n=0..80) ; # _R. J. Mathar_, Jul 20 2007 %Y A089601 Cf. A089591, A089600. %K A089601 nonn,easy,base %O A089601 0,5 %A A089601 _Jeff Erickson_, Dec 31 2003 %E A089601 More terms from _R. J. Mathar_, Jul 20 2007