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%I #11 Sep 03 2017 13:22:52
%S 1,0,2,5,9,4,10,17,25,16,6,17,29,42,56,71,55,38,56,75,95,116,138,161,
%T 185,160,186,213,241,212,242,273,305,338,372,407,443,480,442,481,521,
%U 562,520,563,607,652,698,745,793,842,892,943,995,1048,1102,1047,991
%N a(0) = 1; a(n) = |a(n-1) - n| if n is has already appeared in the sequence, otherwise a(n) = a(n-1) + n.
%p a[0]:=1: S:={1}: for n from 1 to 65 do if member(n,S)=true then a[n]:=abs(a[n-1]-n): S:=S union {a[n]} else a[n]:=a[n-1]+n: S:=S union {a[n]} fi od: seq(a[n],n=0..65); # _Emeric Deutsch_, May 07 2006
%t f[s_] := Block[{n,},n = Length[s]; Return[Append[s, Abs[Last[s] + If[MemberQ[s, n], -n, +n]]]];]; Nest[f, {1}, 66] (* _Ray Chandler_, May 06 2006 *)
%Y Cf. A005132, A118906.
%K easy,nonn
%O 0,3
%A _Leroy Quet_, May 05 2006
%E Extended by _Ray Chandler_ and _Emeric Deutsch_, May 06 2006
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