If I multiply three different prime numbers, the product must have  positive divisors. 
Overseas Competition->Knowledge Point->Number Theory Modules->Prime and Composite Numbers->Determining Prime and Composite Numbers
Multiply the three smallest primes: $$2\times3 \times5=30$$, whose $$8$$ divisors are $$1$$, $$2$$, $$3$$, $$5$$, $$6$$, $$10$$, $$15$$, and $$30$$. 