INTRODUCTION
  A number system defines a set of values used to represent a 
  quantity. We talk about the number of people attending 
  functions, numbers of modules taken per student etc. It is 
  all about quantifying items and values in a relation which 
  helps  to  make  sense  of  our  environment.The  study  of 
  numbers is not only related to computers.
                         A number is a mathematical object used in 
  counting  and  measuring.  The  definition  of  number  has 
  been extended over the years to include such numbers as 
  zero,  negative  numbers,  rational  and  irrational  numbers 
  and complex numbers. 
  CLASSIFICATION 
      OF 
    NUMBERS
                                                            NUMBERS 
        REAL NUMBERS                                                  IMAGINARY NUMBERS
     IRRATIONAL RATIONAL
     NUMBERS    NUMBERS
           FRACTIONS                    INTEGERS
                 NEGATIVE  POSITIVE NUMBERS 
                 NUMBERS   (WHOLE NUMBERS)
                          ZERO                         NATURAL 
                                                             NUMBERS
   TYPES
     OF 
  NUMBERS
        
       1. ODD NUMBERS :-  A number which is not divisible by 2.
              EXAMPLE:- 1,3,5,7,9…….etc.
       2. EVEN NUMBERS :- A number which is divisible by 2.
              EXAMPLE:- 2,4,6,8,10…….etc.
       3. PRIME NUMBERS :- Natural numbers which are divisible by one and the number        
       itself.
               EXAMPLE:- 2,3,5,7,11…….etc.
       4. COMPOSITE NUMBERS :- The number which are not prime are composite numbers.
               EXAMPLE:- 4,6,8,10,12…….etc.
       5. TWIN PRIME :- A twin prime is a prime number that is either 2 less or 2 more than another 
       prime number.
               EXAMPLE:- pair  (41,43), (3,5), (5,7)…….etc.
       6. PRIME TRIPLET :- Set must have the form (p,p+2,p+6) or (p,p+4,p+6) 
               EXAMPLE:- (5,7,11),(7,11,13)…….etc.  
                               except (2,3,5), (3,5,7)
       7. REAL NUMBERS :- The complete set of rational and irrational numbers is the set of real 
       numbers. The real number includes all of the measuring numbers.
       8. RATIONAL NUMBERS :- The number which can be expressed in the form of  are known as 
       rational numbers where p and q are integers and q
       •   When p and q have no common factor other than 1 then rational number  is said to be in 
           standard form.
       •   There are infinitely many rational numbers between two rational numbers.