Question

Explain why 7 X 13 X13 + 13 and 7 X 6 X 5 X 4 X 3 X 2 X 1 + 5 are composite numbers.

Answer 1

7 X 13 X13 + 13

=13(7*13+1)

=13(91+1)

=13*92

where 92 is pdt of prime no.

so, its a composite number.

and

7 X 6 X 5 X 4 X 3 X 2 X 1 + 5

=5(7*6*4*3*2*1+1)

=5(1008+1)

=5(1009)

where 1009 is the pdt of prime numbers.