Explanation:
A natural number is called a prime number (or a prime) if it is bigger than one
and has no divisors other than 1 and itself. (Our solved
example in mathguru.com uses this concept)
For example, 5
is prime, since no number except 1 and 5 divides it. On the other hand, 6 is
not a prime (it is composite), since 6 = 2 · 3.
http://en.wikipedia.org/wiki/Prime_number
Composite number
A composite number is a positive integer which has a positive divisor other than one or itself. In
other words a composite number is any positive integer greater than one that is not a prime number. (Our solved example in mathguru.com uses this concept)
By definition,
every integer greater than one is either a prime number or a composite number. The
number one is a unit - it is neither prime nor composite. For example, the integer 14
is a composite number because it can be factored as 2 × 7. Likewise,
the integers 2 and 3 are not composite numbers because each of them can only be
divided by one and itself.
The first 105 composite numbers are
4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21,
22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48,
49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74,
75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91,
92, 93, 94, 95, 96, (Our
solved example in mathguru.com uses this concept) 98,
99, 100, 102, 104, 105, 106, 108, 110, 111, 112, 114, 115, 116, 117, 118, 119,
120, 121, 122, 123, 124, 125, 126, 128, 129, 130, 132, 133, 134, 135, 136, 138,
140.
http://en.wikipedia.org/wiki/Composite_number
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