#Japt, 8+2=10 8 bytes
ò2_â1Ãxo
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##Explanation :Implicit input of integer U. ò2 :Generate an array of integers from 2 to U, inclusive _ :Passing each number through a function that returns... â : the divisors of the number, 1 : excluding itself. Ã :End function. x :Sum the main array o :by popping the last element from each sub-array. :Implicit output of result