Question

why 7*11*13+13 is composite number

Answer 1

7×11×13 + 13 = 13 (7×11+1) = 13×78 = 13×13×2×3×1

We know that, a composite number is a number which is divisible by numbers other than 1 and itself.

Here, the number 7×11×13 + 13 has factors 1,2,3,13,26,78 etc.. So, it is a composite number.