# Mathematica, 41 bytes #

    FromDigits@*Join@@Reverse@*Range~Array~#&

`Reverse@*Range` is a function that lists the numbers from its input to 1 in descending order. `~Array~#` returns a list of all those lists, with inputs from 1 to the main function's argument. `Join@@` flattens them into a single list, which `FromDigits` converts into a single integer.