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A140266 Inverse permutation to A140265.

%I A140266 #19 Jul 06 2025 14:58:19
%S A140266 1,2,3,6,8,4,7,5,9,18,20,16,24,26,22,12,14,10,19,17,21,13,11,15,25,23,
%T A140266 27,54,56,52,60,62,58,48,50,46,72,74,70,78,80,76,66,68,64,36,38,34,42,
%U A140266 44,40,30,32,28,55,53,57,49,47,51,61,59,63,37,35,39,31,29,33,43,41,45
%N A140266 Inverse permutation to A140265.
%H A140266 Antti Karttunen, <a href="/A140266/b140266.txt">Table of n, a(n) for n = 1..729</a>
%H A140266 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%F A140266 a(n) = Z->N(A117966(n-1)), where Z->N(z) = 2z if z>0 else 2|z|+1.
%o A140266 (Scheme) (string-append (define (A140266 n) (Z->N (A117966 (- n 1))))
%o A140266 (define (Z->N n) (if (positive? n) (* n 2) (+ 1 (* 2 (- n))))))
%o A140266 (Python)
%o A140266 def a117966(n):
%o A140266     if n==0: return 0
%o A140266     if n%3==0: return 3*a117966(n/3)
%o A140266     elif n%3==1: return 3*a117966((n - 1)/3) + 1
%o A140266     else: return 3*a117966((n - 2)/3) - 1
%o A140266 def Z(z): return 2*z if z>0 else 2*abs(z) + 1
%o A140266 def a(n): return Z(a117966(n - 1)) # _Indranil Ghosh_, Jun 07 2017
%Y A140266 Inverse: A140265. a(n) = A140264(n-1)+1.
%K A140266 nonn,look,hear
%O A140266 1,2
%A A140266 _Antti Karttunen_, May 19 2008