Odd number - GCSE Maths Definition

An odd number is a (positive) whole number that cannot be divided exactly by 2. When you divide an odd number by 2, there is always a remainder of 1. The odd numbers are 1, 3, 5, 7, 9, 11, .... They continue to form a sequence with a term-to-term rule of adding 2. As a position-to-term rule, the n^th odd number would be 2n - 1; for example, the 25th odd number is 2 x 25 – 1 = 50 – 1 = 49.

In GCSE Mathematics, recognising odd numbers can help solve problems involving number patterns and sequences.