What are semi-prime numbers?

Semi-prime numbers are numbers made by multiplying two special numbers together, and those special numbers can only be divided evenly by 1 and themselves.

Imagine you have a box of 24 blocks. If you take 6 blocks, that’s half the box, right? But what if you think about it as 8 blocks times 3 blocks, two smaller groups multiplied together to get the whole box? That’s like a semi-prime number!

A semi-prime number is created when you multiply two prime numbers. A prime number is like a special block that can’t be broken down into smaller whole-number blocks, except by 1 and itself.

For example:

• 6 is semi-prime because it’s 2 times 3, and both 2 and 3 are prime.
• 15 is also semi-prime because it’s 3 times 5, and again, both 3 and 5 are prime.

But if you have a number like 12, that's not a semi-prime, it could be 3 times 4, but 4 isn’t a prime number. It can be broken down further into 2 times 2. So 12 has more than just two prime building blocks.