Composite Numbers in Mathematics

What are composite numbers ?

Any number other than 1, which is not a prime number is a composite number.

Thus a composite number is a number which has at least one factor other than 1 and itself.
Every composite number can be written as the product of 2 or more distinct prime numbers.
The number 1 is neither prime nor composite.

Classification based on number of distinct prime factors:

  •  4 = 2 x 2         6=2 x 3
Both, 4 and 6 have prime numbers as their factors (excluding 1 and the number itself). Such numbers which have 2 prime numbers as their factors are called semiprime. One of the factors can even be a square of a prime number.
12 = 2 x 2 x 3
12 is multiple of 2 distinct primes 2 and 3. Thus 12 is also a semi prime number.
  •   30 = 2 x 3 x 5
30 is a multiple of 3 distinct primes, 2, 3 and 5.
Those composite numbers which have 3 distinct prime factors is called a sphenic number.

Classification based on repetition of prime factors:

What are composite numbers?, composite and prime numbers,composite number wikipedia wiki
Composite number

  • 64 = 26
A number in which all prime factors are repeated is called a powerful number. Thus 64 is a powerful number.
  • 210 = 7 x 5 x 2 x 3

When none of the prime factors of a number are repeated, the number is called a squarefree number.

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Also See :- What are Perfect Numbers ?
What is a Co-prime or Relatively prime number ?
Definition of prime number
Properties of Integers