**Natural Numbers:**

· Counting numbers are known as natural numbers. 1, 2, 3, 4, 5,…., etc., are all natural numbers.

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**Theory of Numbers:**

**(1) **Every number is of one of the forms, 5n, 5n ± 1, 5n ± 2.

**(2) **Every square number is of one of the forms 5n, 5n ± 1.

**(3) **The square of every odd number is of the form 8n + 1.

(4) Sum on 'n' consucutive number is always divisible by 'n' if 'n' is odd and sum of 'n' consecutive numbers is never divisible by 'n' if 'n' is even.

Read More...**Methods of Finding Factors:**

**(1) Taking Out Common Factors:** Place the common factor outside as a coefficient and divide each term separately by same factor.

· If ‘a’ is a rational number and ‘n’ is a positive integer such that the nth root of ‘a’ is an irrational number, then a^{1/n} is called a surd e.g., Ö Read More...