Different kinds of Numbers

Perfect number -number whose divisors (except itself) add up to itself. For example,. 28 is a perfect number. Its proper divisors are {1, 2, 4, 7, 14} and 1 +2 +4 +7 +14 = 28. Can you find the smallest perfect number?

Deficient number -number whose proper divisors add up to less than itself. For example, 16 is a deficient number as sum of its proper divisors {1, 2, 4, 8} = 15.

Abundant number -number whose proper divisors add up to more than the number itself. For example, 18 is a abundant number as 1+2 +3 +6 +9 = 21. Can you find the smallest abundant number?

Square number -number that can be formed by counting the number of objects used in making a square

1 is a square number.

4 is a square number.

9 is a square number.

Can you find the next three square numbers?

Triangular number -number that can be formed by counting the number of objects used in making a triangle.

1 is a triangular number
3 is a triangular number
6 is a triangular number

Can you find the next three triangular numbers?

Happy number -number for which the sum of the squares of the digits eventually equals 1.For example, 203 is happy because 2² +0² +3² = 13; 1² +3² = 10; 1² +0² = 1

Can you think of another happy number? An unhappy number?

Narcissistic number -like self centered persons, the narcissistic numbers are integers equal to an expression using the same digits. For example, 36 is narcissistic as 36 = 3! × 6

Sometimes, narcissistic number is defined as a number equal to the sum of its digits raised to a certain power (mostly the number of digits in the number).

           371 is narcissistic as 371 = 3³ +7³ +1³

 Can you think of another narcissistic number?

Palindromic number -number having same digits forward and backward e.g. 121, 102201, 8523258 etc.

Prime number -numbers which have on other divisors than 1 and itself . 2, 3, 5, 7, 11, 13, 17,.......... etc. are prime numbers. They have fascinated mathematicians since ages.

Other kind of numbers -Transcendental numbers (Liouville numbers), Vulgar numbers (Irrational numbers), Cyclic numbers, Sociable numbers, Fibonacci numbers, Amicable numbers, Coprime numbers, Figurate numbers, Weird numbers etc.

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Some special numbers:

 0 : Zero Discovered by Indians. Read more at The story of zero

 2 : The only even Prime

2 : Black money -

 :  (sade sati -) denotes misery and suffering

 007 : Spy (of James Bond variety)

  10 : (Fraud -)

  13 : Lucky in some countries, unlucky in some. Many hotels in Europe don't have room number 13.

  16 : Sweet sixteen

 420 : All Indians are aware of this section on cheating in Criminal Code.

 666 : The number of the beast.

 786 : Lucky number for Muslims. Amitabh Bachhan wore batch number 786 in "Coolie".

1729 : Number associated with Ramanujan.