In (1 + x) + (1 + x) 2 + +In the expansion of (1 + x) 6, the coefficient of term X2 is______ (answer with numbers)

In (1 + x) + (1 + x) 2 + +In the expansion of (1 + x) 6, the coefficient of term X2 is______ (answer with numbers)

(1+x)+(1+x)2+… +In the expansion of (1 + x) 6, the coefficient of term X2 is C22 + C32 + C42 + +C62=C33+C32+C42+… +C62=C43+C42+… +C62=… =C63 = 35, so the answer is 35