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A321726 Reverse each run of nonzero digits in ternary expansion of n and convert back to decimal. 2

%I

%S 0,1,2,3,4,7,6,5,8,9,10,11,12,13,22,21,16,25,18,19,20,15,14,23,24,17,

%T 26,27,28,29,30,31,34,33,32,35,36,37,38,39,40,67,66,49,76,63,64,65,48,

%U 43,70,75,52,79,54,55,56,57,58,61,60,59,62,45,46,47,42,41

%N Reverse each run of nonzero digits in ternary expansion of n and convert back to decimal.

%C This sequence is a self-inverse permutation of nonnegative integers.

%H Rémy Sigrist, <a href="/A321726/b321726.txt">Table of n, a(n) for n = 0..19683</a>

%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>

%F a(3 * n) = 3 * a(n).

%e For n = 3497:

%e - the ternary representation of 3497 is "11210112",

%e - we replace "1121" by "1211" and "112" by "211" and obtain "12110211",

%e - hence a(3497) = 3991.

%t rernz[n_]:=FromDigits[Flatten[If[FreeQ[#,0],Reverse[#],#]&/@SplitBy[ IntegerDigits[ n,3],#!=0&]],3]; Array[rernz,70,0] (* _Harvey P. Dale_, Nov 15 2020 *)

%o (PARI) a(n, base=3) = my (d=digits(n*base, base), nz=0); for (i=1, #d, if (d[i], nz++, if (nz, for (j=1, floor(nz/2), [d[i-j],d[i-nz-1+j]] = [d[i-

%o nz-1+j],d[i-j]]); nz=0))); fromdigits(d, base)/base

%Y See A321464 for a similar sequence.

%K nonn,base,look

%O 0,3

%A _Rémy Sigrist_, Nov 17 2018

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Last modified September 20 05:24 EDT 2021. Contains 347577 sequences. (Running on oeis4.)