1 (one)
The number 1 has a special place under the odd numbers.
Explanation
Natural numbers can be divided into even and odd numbers.
Natural numbers Even numbers Special number: 0 Composite numbers Squares of even numbers
No perfect squaresOnly prime number: 2 Odd numbers Special number: 1 Composite numbers Squares of odd numbers
No perfect squaresPrime numbers 4n + 1 prime
4n + 3 prime