- Perfect numbers
A perfect number is one that equals the sum of its proper divisors (except the
number itself as a divisor). Note that the proper divisors include all the divisors of
the number considered, excepting the given number.
For example, 6 = 3+2+1
28 = 14+7+4+2+1
Observe that in both the cases mentioned above the sum of all the divisors of the
number considered equals the given number. Hence such numbers are called perfect
numbers.
- Greatest Common Divisor
Two numbers may have several common divisors. The greatest of all the common
divisors is called the Greatest Common Divisor (G.C.D) of the numbers. G.C.D is also
known as the Highest Common Factor (H.C.F).
To find out the G.C.D. of 12 and 16, list the divisors of 12, list the divisors of 16 and
then select the greatest common divisor
Divisors of 12 : 1, 2, 3, 4, 6, 12
Divisors of 16 : 1, 2, 4, 8, 16
Common divisors : 1, 2, 4
1’s
2’s
3’s
4’s
6’s
12’s
