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%I #26 Apr 15 2024 09:48:17
%S 0,3,6,1,4,7,2,5,8,9,12,15,10,13,16,11,14,17,18,21,24,19,22,25,20,23,
%T 26,27,30,33,28,31,34,29,32,35,36,39,42,37,40,43,38,41,44,45,48,51,46,
%U 49,52,47,50,53,54,57,60,55,58,61,56,59,62,63,66,69,64,67,70,65,68,71,72
%N Exchange rightmost two ternary digits of n > 1; a(0)=0, a(1)=3.
%C Self-inverse permutation of natural numbers: a(a(n)) = n.
%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>.
%H <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,1,-1).
%F From _R. J. Mathar_, Oct 12 2010: (Start)
%F a(n) = a(n-1) + a(n-9) - a(n-10) = 9 *floor(n/9) + 3*(n mod 3) + (floor(n/3) mod 3).
%F G.f.: x*(3 + 3*x - 5*x^2 + 3*x^3 + 3*x^4 - 5*x^5 + 3*x^6 + 3*x^7 + x^8) / ( (1+x+x^2)*(x^6+x^3+1)*(x-1)^2 ). (End)
%e a(10) = a(101_3) = 110_3 = 12.
%e a(20) = a(202_3) = 220_3 = 24.
%e a(30) = a(1010_3) = 1001_3 = 28.
%Y Cf. A007089, A080412.
%K base,easy,nonn,changed
%O 0,2
%A _Jonathan Vos Post_, Oct 03 2010
%E Corrected and extended by _D. S. McNeil_, Oct 06 2010
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