### A number is odd if it is not divisible by 2.

#### The number 22,222,222,209 is odd, because it is not divisible by 2: the remainder is 1 when divided by 2.

#### How to recognize an odd number: its last digit, the one that is in the ones place (the first digit of the number counted from the right), is: 1, 3, 5, 7 or 9.

#### Mathematically, the odd numbers can be written as:

2 × k + 1, where k ∈ Z, the set of integer numbers

## The number 22,222,222,209 is odd.

## Operating rules (scroll down...)

### When working with even and odd numbers, the following rules apply:

#### Addition:

even + even = even; even + odd = odd; odd + odd = even

Examples:

2 + 4 = 6 (even); 1 + 2 = 3 (odd); 1 + 3 = 4 (even).

#### Subtraction:

even - even = even; even - odd = odd; odd - odd = even

Examples:

4 - 2 = 2 (even); 2 - 1 = 1 (odd); 3 - 1 = 2 (even).

#### Multiplying:

even × even = even; even × odd = even; odd × odd = odd

Examples:

2 × 4 = 8 (even); 2 × 3 = 6 (even); 3 × 5 = 15 (odd).