Question: 1 20 has exactly 5 factors?
Answer: 8 has four factors {1,2,4,8} ; 12 has six factors {1,2,3,4,6,12} ; 16 has five factors {1,2,4,8,16} : 18 has six factors {1,2,3,6,9,18} and 20 has six factors {1,2,4,5,10,20} .