Return a list of all integer factors of posittive n:
abjad> mathtools.factors(84)
[1, 2, 2, 3, 7]
abjad> for n in range(10, 20):
... print n, mathtools.factors(n)
...
10 [1, 2, 5]
11 [1, 11]
12 [1, 2, 2, 3]
13 [1, 13]
14 [1, 2, 7]
15 [1, 3, 5]
16 [1, 2, 2, 2, 2]
17 [1, 17]
18 [1, 2, 3, 3]
19 [1, 19]
Raise TypeError on noninteger n:
abjad> mathtools.factors(7.5)
TypeError
Raise ValueError on nonpositive integer n:
abjad> mathtools.factors(-1)
ValueError