Question

explain why 3×5×13×17+17×7 is composite number​

Answer 1

3×5×13×17+17×7
3315+119
3434

here in 1st and 2nd place no. is similar as 3rd and 4th no.
therefore it is composite no.

Answer 2

Recall that prime numbers are the numbers which have two factors, i.e., 1 and the number itself. For example, 7 is a prime number, because it has only two factors, 1 and 7 (the number itself).

Composite number is a number having more than two factors.

3×5×13×17×17×7=394485

394485 is a composite number, since it is having more than two factors.

Factors of 394485=1,3,5,7,13,15,17,21,35,39,51,65,85,91,105,119,195,221,255,,273,289.....

As you can see, 394485 is a composite number, since it is having more than two factors.