The coefficient of x20 in the expansion of 1+11!x+12!x2+…+120!x203is

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320!

32020!

60C20

answer is C.

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Detailed Solution

Note that, coefficient of x20 in 1+11!x+12!x2+…+120!x203coefficient of x20 in 1+11!x+12!x2+…+120!x20+121!x21+…3coefficient of x20 in e3x=32020!

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