(2020 Putnam Exam, problem A1)
How many positive integers N satisfy all of the following 3 conditions:
(i) N is
divisible by 2020
(ii) N has
at most 2020 decimal digits
(iii) The
decimal digits of N are a string of consecutive ones followed by a string of
consecutive zeros.
Note: This only requires pre-college level mathematics, but like most Putnam problems it is not easy.
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