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%I #13 Oct 19 2017 03:14:12
%S 1,2,5,3,8,11,4,6,14,17,20,9,23,7,26,12,29,32,35,10,15,38,40,43,18,46,
%T 13,21,49,52,55,58,24,16,61,64,27,67,70,72,19,30,75,77,33,80,22,36,83,
%U 86,89,92,95,25,39,98,101,41,104,28,44,107,110,113,116,47,119,31,122
%N Inverse permutation to A081145.
%H Reinhard Zumkeller, <a href="/A081146/b081146.txt">Table of n, a(n) for n = 1..10000</a>
%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%t f[s_] := Block[{d = Abs[Rest@s - Most@s], k = 1}, While[ MemberQ[d, Abs[k - Last@s]] || MemberQ[s, k], k++ ]; Append[s, k]]; t = Nest[f, {1}, 130]; Table[ Position[t, n], {n, 70}] // Flatten (* _Robert G. Wilson v_, Jun 09 2006 *)
%t f[s_] := Block[{k = 1, d = Abs[Most@s - Rest@s], l = Last@s}, While[MemberQ[s, k] || MemberQ[d, Abs[l - k]], k++ ]; Append[s, k]]; t = Nest[f, {1}, 125]; Table[Position[t, n], {n, 71}] // Flatten (* _Robert G. Wilson v_, Jun 13 2006 *)
%o (Haskell)
%o import Data.List (elemIndex); import Data.Maybe (fromJust)
%o a081146 = (+ 1) . fromJust . (`elemIndex` a081145_list)
%o -- _Reinhard Zumkeller_, Jul 02 2015
%Y Cf. A081145.
%K nonn
%O 1,2
%A _Don Reble_, Mar 08 2003
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