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%I #13 Mar 14 2017 03:43:07
%S 1,3,2,6,5,7,4,12,11,9,13,10,16,15,8,24,23,21,18,19,20,22,17,31,30,28,
%T 25,29,14,46,45,43,40,36,27,42,37,32,44,38,35,49,48,41,47,33,61,60,58,
%U 55,51,34,72,71,69,66,62,53,57,52,67,59,56,70,64,50,84,83,81,78,74,54
%N a(1) = 1. a(n) = (|a(n-1) - n| + 1)th positive integer which does not occur earlier in the sequence.
%C This sequence is likely a permutation of the integers.
%H Ivan Neretin, <a href="/A118833/b118833.txt">Table of n, a(n) for n = 1..10000</a>
%e The first 8 terms of the sequence are 1,3,2,6,5,7,4,12. |a(8) - 9| + 1 = 4, so a(9) = the 4th positive integer which doesn't occur earlier in the sequence (i.e., the 4th integer in the sequence 8, 9, 10, 11, 13, 14, ...). Therefore a(9) = 11.
%t Fold[Append[#1, Complement[Range[Max[#1] + (d = Abs[#1[[-1]] - #2] + 1)], #1][[d]]] &, {1}, Range[2, 72]] (* _Ivan Neretin_, Mar 13 2017 *)
%Y Cf. A118834.
%K easy,look,nonn
%O 1,2
%A _Leroy Quet_, May 01 2006
%E More terms from _Franklin T. Adams-Watters_, Nov 28 2006
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