Beware of bugs in the above code; I have only proved it correct, not tried it. Donald E. Knuth
Prime Number is a number which can be divided evenly only by 1, or itself. The prime number has only two divisors, 1 and same number. Prime numbers mainly used in public key cryptography. Example:- 13 We can divide only by 1 or 13. 13 doesn't have any other divisor. So, it is a prime number. 12 We can divide 1, 2,3,4,6. 12 has many divisors. So, it is not a prime number.
Print the first 20 primenumbers :1 2 3 5 7 11 13 17 19