A118906 a(0) = 1; a(n) = |a(n-1) - n| if n is not one of the earlier terms of the sequence, otherwise a(n) = a(n-1) + n.

1, 2, 4, 1, 5, 10, 4, 3, 5, 4, 14, 3, 9, 4, 18, 3, 13, 4, 22, 3, 17, 4, 26, 3, 21, 4, 30, 3, 25, 4, 34, 3, 29, 4, 38, 3, 33, 4, 42, 3, 37, 4, 46, 3, 41, 4, 50, 3, 45, 4, 54, 3, 49, 4, 58, 3, 53, 4, 62, 3, 57, 4, 66, 3, 61, 4, 70, 3, 65, 4, 74, 3, 69, 4, 78, 3, 73, 4, 82, 3, 77, 4, 86, 3, 81, 4

Offset

0,2

Links

Table of n, a(n) for n=0..85.

Maple

a[0]:=1: S:={1}: for n from 1 to 100 do if member(n, S)=false 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..100); # Emeric Deutsch, May 07 2006

Mathematica

f[s_] := Block[{n, }, n = Length[s]; Return[Append[s, Abs[Last[s] + If[MemberQ[s, n], +n, -n]]]]; ]; Nest[f, {1}, 100] (* Ray Chandler, May 06 2006 *)

Crossrefs

Cf. A005132, A118907.

Sequence in context: A201283 A283739 A080427 * A085059 A336164 A181336

Adjacent sequences: A118903 A118904 A118905 * A118907 A118908 A118909

Keyword

easy,nonn

Author

Leroy Quet, May 05 2006

Extensions

Extended by Ray Chandler and Emeric Deutsch, May 06 2006

Status

approved