#Ruby, 28 bytes#

 ->n{eval('['*n+'n'+']*n'*n)}

Stolen shamelessly from [xnor][1]'s [excellent answer][2].

 [1]: http://codegolf.stackexchange.com/users/20260/xnor
 [2]: http://codegolf.stackexchange.com/a/111696/58437