
Prime numbers
A prime number has only two factors,
itself and 1.
e.g {2, 3, 5, 7, 11, 13, 17,
19, 23, 29, 31, 37, 41, 43...}
23 is a prime number because
it has only two factors, 1 and itself, 23.

Fermat Numbers
These are numbers of the form + 1 where n is a positive integer:
when n = 0 this gives the first Fermat number
2^{1} + 1 = 3
when n = 1 this gives the second Fermat number
2^{2} + 1 = 5
when n = 2 this gives the third Fermat number
2^{4} + 1 = 17
when n = 3 this gives the fourth Fermat number
2^{8} + 1 = 257 and so on...

Fibonacci Numbers
These numbers belong to the sequence { 1, 1,
2, 3, 5, 8, 13, 21...} where each number is the sum of the two numbers
before it.
1st term = 1
2nd term = 1
3rd term = 1+ 1 = 2
4th term = 1 + 2 = 3 and so on...

Perfect Numbers
A perfect number is a counting number which
equals the SUM of all its factors except itself.
e.g. 6 is a perfect number. Factors are {1,
2, 3, 6} Sum of factors (except 6) = 6
28 is a perfect number. Factors are {1, 2, 4,
7, 14, 28} Sum of factors (except 28) = 28

Triangle number
A triangle number is the number that can be
shown as a pattern of dots in the shape of a triangle.
i.e. {1, 3, 6, 10, 15, 21, 28, 36, 45...}
First triangle number is 1
Second triangle number is 3
Third triangle number is 6
Fourth triangle number is 10

Composite Number
A composite number is a number with more than
two factors. i.e. The nonprime numbers
i.e. 4, 6, 8, 9, 10, 12, 14...

Platonic Solids
There are only FIVE polyhedra which have every
face the same regular polygon.
These are:
 tetrahedron (4 faceseach a triangle)
 cube (6 faceseach a square)
 octahedron (8 faceseach a triangle)
 dodecahedron (12 faceseach a pentagon)
 icosahedron (20 faces each a triangle)

Palindrome
A number (or word) which reads the
same backwards e.g. 34543, 44, 1000001

Factorial (n!)
The factorial of a positive integer
n is the product of all the positive integers up to and including
n . For example: 6! = 5 x 4 x 3 x 2 x 1 = 720

