Prime Numbers Explained Simply
A prime number is a number greater than 1 that can only be divided evenly by 1 and by itself.
đź’¬ Mia asks Grandpa Theo
Why isn't 1 a prime number? It can also only be divided by 1!
Good question! Mathematicians deliberately decided to exclude 1 - otherwise many important calculation rules wouldn't work cleanly anymore.
And how do I find out if, say, 17 is a prime number?
You simply try, one after another, whether 2, 3, 5, 7 ... divide it evenly. For 17, none of them work - so 17 is a prime number!
Is 15 a prime number? No: 15 = 3 × 5, so it can also be divided by 3 and by 5 - not just by 1 and itself.
Prime numbers are essentially the "building blocks" of all numbers: every natural number greater than 1 can be uniquely written as a product of primes (e.g. 12 = 2 × 2 × 3). That's why they're so important in mathematics - and even in encrypting data on the internet.
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