Putnam 2020 A1
Source: 81st William Lowell Putnam Competition
February 22, 2021
PutnamPutnam 2020
Problem Statement
How many positive integers satisfy all of the following three conditions?\\
(i) is divisible by .\\
(ii) has at most decimal digits.\\
(iii) The decimal digits of are a string of consecutive ones followed by a string of consecutive zeros.