Answer: 6
I don't know what a hundred chart is but every prime bigger than 3 is one more or one less than a multiple of six.
The possible remainders when we divide by six are 0,1,2,3,4 and 5. The remainders 0,2,3, and 4 all indicate we have a multiple of two or three, so composite if bigger than 3. So the only possible remainders are 1 and 5, which are one more and one less than a multiple of six respectively.
