<prompt> Nambari 1, 3, 6, 10, ldets, zinaitwa nambari za pembetatu, kama inavyoonyeshwa kijiometri hapa. 20textth nambari ya pembetatu ni nini?asynukta 0,0;lebo1,0,-1.5;nukta 3,0;nukta 4,0;nukta 3,1;lebo3,3.5,-1.5;nukta 7,0;nukta 8,0;nukta 9,0;nukta 7,1;nukta 7,2;nukta 8,1;lebo6,8,-1.5;nukta 12,0;nukta 13,0;nukta 14,0;nukta 15,0;nukta 12,1;nukta 13,1;nukta 14,1;nukta 12,2;nukta 13,2;nukta 12,3;lebo10,13.5,-1.5;asy  <response>: Nambari ya pembetatu ya 20 ni 1 2 3 cdots 20 frac20212 210. 