A lucky year is one in which at least one date, when written in the form day/month/year, has the following property. The product of the month times the day equals the last two digits of the year. For example, 1956 is a lucky year because it has the date 7 / 8 / 56 where $$7 \times 8 = 56$$, but 1962 is not a lucky year as $$62 = 62 \times 1$$ or $$31 \times 2$$, where 31/2/1962 is not a valid date. From 1900 to 2018 how many years are not lucky (not including 1900 and 2018)? Give proper explanation for your answer.