1 2 3

When people says it is "as easy as 1 2 3", it means that it is very simple. The numbers "1 2 3" are referenced in more places that you can imagine. Here is a list of them

1. 1, 2, and 3 are whole numbers or integers.

2. They can only be divided by itself or divide by 1. (They are not all prime numbers. The number 1 is actually not considered as Prime number.)

3. They are stepped increments of 1. 

4. If you add or minus two of them you will get the third as a result. 1+2=3. 3-1=2, 3-2=1.

5. They are next three sequence of Fibonacci Number starting from 1.

6. People always use 1, 2, 3 as a signal to start something.

7. A chart pattern called 1-2-3 formation is used in liquid markets.

8. People always say "testing 1 2 3" to test microphones.

9. Foxtrot dance is 4/4 time signature but dancers often use 1_23 (slow, fast, fast) to teach the rhythm.

10. Waltz dancers usually learn the steps as 123.

11. The first few numbers in a Partition Function is 123.

12. It is the first few numbers of "Square free numbers".

13. If you search https://oeis.org for "1,2,3", you get 1659 pages of integer sequences that contains the numbers.

14. If you search Google for "1,2,3" you get about 25,270 million results.