How many integers less than 100 have exactly 4 odd factors but no even factors?
Choose the correct choice from the following answers:
A) 11	B) 13	C) 15	D) 17	E) 19
Two cases are possible:   x1y1=xy=odd&lt;100x1y1=xy=odd&lt;100, where xx and yy are odd prime numbers, then # of factors will be (1+1)(1+1)=4(1+1)(1+1)=4;   If x=3, then y can be: 5, 7, 11, 13, 17, 19, 23, 29, 31 - 9 numbers.   If x=5, then y can be: 7, 11, 13, 17, 19 - 5 numbers.   If x=7, then y can be: 11, 13 - 2 numbers.   OR:   x3=odd&lt;100x3=odd&lt;100, where xx is odd prime number, then # of factors will be (3+1)= 
<gadget id="calculator">(3+1)</gadget>
<output>4</output>
4(3+1)=4.   x can be only 3 - 1 number.   Total 9+5+2+1=179+5+2+1=17 .   Answer: 17.
<result>D</result>
How many integers less than 100 have exactly 4 odd factors but no even factors?