The number 7 is odd.
A number is odd if it is not divisible by 2.
The number 7 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 is 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
Operating rules
When working with even and odd numbers, the following rules apply:
Addition: even + even = even; even + odd = odd; odd + odd = even.
Subtraction: even - even = even; even - odd = odd; odd - odd = even.
Multiplying: even × even = even; even × odd = even; odd × odd = odd.
Other operations of the same kind: