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%I #15 Jun 10 2017 12:09:45
%S 0,1,2,5,7,3,6,4,8,17,19,15,23,25,21,11,13,9,18,16,20,12,10,14,24,22,
%T 26,53,55,51,59,61,57,47,49,45,71,73,69,77,79,75,65,67,63,35,37,33,41,
%U 43,39,29,31,27,54,52,56,48,46,50,60,58,62,36,34,38,30,28,32,42,40,44
%N Inverse permutation to A140263.
%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%F a(n) = A140266(n+1)-1.
%o (Scheme:) (define (A140264 n) (- (A140266 (+ 1 n)) 1))
%o (Python)
%o def a117966(n):
%o if n==0: return 0
%o if n%3==0: return 3*a117966(n/3)
%o elif n%3==1: return 3*a117966((n - 1)/3) + 1
%o else: return 3*a117966((n - 2)/3) - 1
%o def Z(z): return 2*z if z>0 else 2*abs(z) + 1
%o def a140266(n): return Z(a117966(n - 1))
%o def a(n): return a140266(n + 1) - 1 # _Indranil Ghosh_, Jun 07 2017
%Y Inverse: A140263.
%K nonn
%O 0,3
%A _Antti Karttunen_, May 19 2008
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