%I #7 Oct 26 2023 22:58:08
%S 18,19,20,21,22,23,24,25,26,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,
%T 17,45,46,47,48,49,50,51,52,53,27,28,29,30,31,32,33,34,35,36,37,38,39,
%U 40,41,42,43,44,72,73,74,75
%N Tersum n + 18.
%F Tersum m + n: write m and n in base 3 and add mod 3 with no carries; e.g., 5 + 8 = "21" + "22" = "10" = 1.
%K nonn
%O 0,1
%A _N. J. A. Sloane_
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