How many integers $n$ with $70 \leq n \leq 90$ can be written as $n = ab + 3a + 8b$ for at least one ordered pair of positive integers $(a, b) \, ?$
ab + 3a + 8b
a b n
11 2 71
4 5 72
6 4 74
3 6 75
2 7 76
9 3 78
5 5 80
7 4 81
4 6 84
3 7 86
6 5 88
11 3 90
+1439 
