if An =(111111----1) where n denotes the no. of 1 nw if n is even then , it is clearly seen that pair of two ones is divisible by 11 so the no .of ones is even v can make pair of two ones i.e it can be divisible by 11 thus A480 is not prime nd A912 is not prime hope u got it..... thanks.........
Moderation Team
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