%I

%S 12,13,14,15,16,17,9,10,11,21,22,23,24,25,26,18,19,20,3,4,5,6,7,8,0,1,

%T 2,39,40,41,42,43,44,36,37,38,48,49,50,51,52,53,45,46,47,30,31,32,33,

%U 34,35,27,28,29,66,67,68,69

%N Tersum n + 12.

%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_.