explain

A number is a composite number if it has factors other than 1 and itself.

 

Now, 7x 11x 13+13 = 13 (7 x 11 +1) = 13 x 78.

This number has factors like 2, 3 and 13 as its factors other than 1 and itself. Hence it is a composite number.

 

7 x 6 x 5 x 4 x 3 x 2 x 1 + 5 = 5 (7 x 6 x 4 x 3 x 2 x 1 + 1) = 5 x 1009

This number has factors other than 1 and itself (Viz. 5). Hence, it is a composite number.