A = 1 + 5 + 52 + 53 +...+ 52016 + 52017
5A = 5 + 52 +...+ 52016 + 52017 + 52018
4A = (5 + 52 +...+ 52016 + 52017 + 52018 ) - ( 1 + 52 + 53 +...+ 52016 + 52017 )
4A = 52018 - 1
A = 52018 - 1 /4
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dòng cuối ý mik là 52018 - 1 chia cho 4