'Extend to include the ith prime number.
i must be an integer.
The list is extended by 50% if it is too short, so it is
likely that it will be longer than requested.
Examples
>>> from sympy import sieve
>>> sieve._reset() # this line for doctest only
>>> sieve.extend_to_no(9)
>>> sieve._list
array(\'l\', [2, 3, 5, 7, 11, 13, 17, 19, 23])'

def extend_to_no(self, i):

    i = as_int(i)
    while (len(self._list) < i):
        self.extend(int((self._list[(-1)] * 1.5)))
