# Number System Short Notes

- Number 1 is neither divisible nor prime.
- Two consecutive odd prime numbers are called prime pair.
- All natural numbers are whole, rational, integer and real.
- All whole numbers are rational Integer and real.
- All whole numbers are rational and real.
- All rational numbers includes the integers, since every integer can be written as a fraction with denominator 1. Example (7/1) not only 7
- All whole numbers, rational and irrational numbers are real.
- Natural (including Prime, Composite, even or odd) numbers and whole numbers are never negative.
- Any Prime Number can never be a Composite Number.
- Fractions are rational.
- All prime number except 2 are odd. Or 2 is the only even prime number.
- Zero (0) is neither negative nor positive number.
- If a is any number then, if a divides zero, result will be zero. If 0 divides a, then result will be infinite or not defined or undetermined i.e.

0/a =0, but a/0 =∞ (infinite)

where a is real number.
- The sum and the product of two rational number is always a rational numbers.
- The product or the sum of a rational number and irrational number is always an irrational number.
- Pie (π) is an irrational number.
- There can be infinite number of rational or irrational numbers between two rational numbers or two irrational numbers.
- Decimal indication of an irrational number is infinite coming. as−√3,√2as−3,2The square of an even is even and the square of an odd number is odd.

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