What is even or odd?

Answer 1

Alternate number sequence.

Numbers ending in 0,2,4,6,8 are EVEN

Numbers ending in 1,3,5,7,9 are ODD

Hence

0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20 et seq..,,

Are alternative Even and Odd.

e.g. A number such as 1213 is Odd because it ends in ;3;

A number such as 1,234,568 is Even because it ends in '8'.

Answer 2

any number ending in 1,3,5,7,9 is odd.

any number ending in 2,4,6,8,0 is even.

zero by itself is not a special case and is also even. See "The Parity of Zero" in the Related Links section.