%I A004493
%S A004493 4,5,3,7,8,6,1,2,0,13,14,12,16,17,15,10,11,9,22,23,21,25,
%T A004493 26,24,19,20,18,31,32,30,34,35,33,28,29,27,40,41,39,43,
%U A004493 44,42,37,38,36,49,50,48,52,53,51,46,47,45,58,59,57,61
%N A004493 Tersum n + 4.
%F A004493 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.
%F A004493 a(n)= -9 + Sum_{k=0..n}{(1/36)*(-59*(k mod 9)+13*((k+1) mod 9)-23*((k+2) 
               mod 9)+13*((k+3) mod 9)+13*((k+4) mod 9)+13*((k+5) mod 9)-23*((k+6) 
               mod 9)+13*((k+7) mod 9)+49*((k+8) mod 9)},with n>=0 - Paolo P. Lava 
               (ppl(AT)spl.at), Dec 03 2007
%Y A004493 Sequence in context: A069197 A021692 A107793 this_sequence A019836 A020503 
               A071992
%Y A004493 Adjacent sequences: A004490 A004491 A004492 this_sequence A004494 A004495 
               A004496
%K A004493 nonn
%O A004493 0,1
%A A004493 N. J. A. Sloane (njas(AT)research.att.com).