0,1

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.

a(n)= -4 + Sum_{k=0..n}{(1/36)*(-35*(k mod 9)+((k+1) mod 9)+((k+2) mod 9)+((k+3) mod 9)+((k+4) mod 9)-35*((k+5) mod 9)+37*((k+6) mod 9)+((k+7) mod 9)+37*((k+8) mod 9)},with n>=0 - Paolo P. Lava (ppl(AT)spl.at), Dec 03 2007

Sequence in context: A008938 A021600 A046256 this_sequence A113786 A004487 A010500

Adjacent sequences: A004492 A004493 A004494 this_sequence A004496 A004497 A004498

nonn

N. J. A. Sloane (njas(AT)research.att.com).