MR-832 / 1503. problem

Determine the limit value of the series:

 an=1+3nn

limn→∞1+3nn

3n=1t

3·t=n

n→∞t→∞

limt→∞1+1t3·t

=limt→∞1+1tt3

=limt→∞1+1tt3

=e3