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Basic information
Q What is a prime number?
Answer: A number divisible by it self and by one only.
If it is divisible by any number it is not prime.
Example: 2, 3, 5, 7, 11, 13, 17, etc…..
 

Q What are the prime numbers till 100?
2, 3, 5,7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.
 

Things to keep in mind!
• A number ending with 0, 2(only the first one), 4, 5(only the first one), 6, 8.
• Numbers ending with 1, 3, 7, 9 have chance to be a prime number.
• If a number divided by a number and the answer is a whole number so the number is not prime.
Example: 2603/19=137- Definition-(A no. which is not prime*A no. which is prime= to a whole no.)
This means that the number is not a prime number.
• If a number divided by a number and the answer is a decimal so you go to the next number (it is according to the numbers value) and if it is not divisible by any of the numbers (it is according to the numbers value), so, it is prime.
Example: 0-500(a number below this should be divided by only 3, 7, 11, 13, 17 & 19) . . . 259/3=86.33. . . . . . . .
259/7=37
This means that the number 259 is not a prime!