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2\1+(3\1+3\2)+(4\1+4\2+4\3)+.+(40\1+40\2+.+40\38+40\39) =1/2+2/2+3/2+4/2+5/2+5/2+...+39/2 =(1+2+3+...+39)/2 =[(1+39)*39/2]/2 =390.
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