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Triangular number, I cant figure it out. Because I really need to find out for my answer
It is 1+2+3+4+5+ ... +198+199+200 if you pair up numbers at either end of the line ... 1 and 200, 2 and 199, 3 and 198, etc you will get 100 pairs, and each pair will add to 201 ... So your answer will be 100 x 201 = 20,100
