What are happy numbers?

A happy number is one that eventually reaches 1 when you keep adding up the squares of its digits, like a fun game that always ends in joy.

Imagine you have a favorite toy box, and every time you play with your toys, you count how many there are. Now, think of a happy number as a special toy box where, no matter how many times you mix up the toys and count them again, you always end up with just one toy, that's 1, the happiest number of all!

Here’s how it works:

Start with any number, say 7.

• Square each digit (7 becomes $7^2 = 49$)
• Add those squares together: 4 + 9 = 13
• Repeat with 13: $1^2 + 3^2 = 1 + 9 = 10$
• Then with 10: $1^2 + 0^2 = 1 + 0 = 1$

Once you hit 1, that number is a happy number, it’s like your toy box finally having just one perfect toy.

If instead, you end up in a never-ending cycle without reaching 1, then it's not a happy number, more like a toy box that keeps changing toys forever!