Odd numbers and Even numbers.

Odd numbers

Any integer that can not be divided exactly by 2.

" (2n-1) "

n=1 => 2*1-1=1

n=2 => 2*2-1=3

n=3 => 2*3-1=5

(1,3,5,7,9......................2n-1)

Even numbers.

Even numbers can be divided evenly into groups of 2

"2n"

n=1 => 2*1 =2

n=2 => 2*2 =4

n=3 => 2*3 =6

(2,4,6,8,10........................2n)