Even and Odd
An even number is an integer that is divisible by 2 and an odd number is an integer that is not divisible by 2. Thus 2, 4, 6, 8... are even numbers and 1, 3, 5, 7... are odd numbers. Any even number can be written as 2n where n is an integer and any odd number can be written as 2n + 1 or as 2n - 1, where n is an integer.
The sum, difference, or product of even numbers is an even number. On the other hand, the product of odd numbers is odd, but the sum or difference of two odd numbers is even.
Science EncyclopediaScience & Philosophy: Ephemeris to Evolution - Historical Background