%I

%S 9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,0,1,2,3,4,5,6,7,

%T 8,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,27,28,29,30,

%U 31,32,33,34,35,63,64,65,66

%N Tersum n + 9.

%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_.