Ta có : A = 5 + 52 + 53 + ...... + 52016
=> 5A = 52 + 53 + 54 + ........ + 52017
=> 5A - A = 52017 - 5
=> 4A = 52017 - 5
=> 4A + 5 = 52017
=> n = 2017
A = 5 + 52 + 53 + ... + 52016
5A = ( 5 + 52 + 53 + ... + 52016 ) x 5
5A = 52 + 53 + 54 + ... + 52017
5A - A = ( 52 + 53 + 54 + ... + 52017 ) - ( 5 + 52 + 53 + ... + 52016 )
4A = 52017 - 5
A = \(\frac{5^{2017}-5}{4}\)
4N + 5 = 5n
52017 - 5 + 5 = 5n
52017 + ( 5 - 5 ) = 5n
52017 + 0 = 5n
52017 = 5n
=> n = 2017