how 2 find out the prime numbers ?is there any direct formula/e?

Answer 1

if there was a direct formula for all prime numbers, then a big part of cryptology would crumble (you wouldn't be able to encrypt data as easily).

However, if you want to get a big prime number, then you should be glad to know that some formulas like (2^n)-1 give you a "good chance" of getting a prime. (but NOT ALWAYS, since 3*5=15=16-1=2^4-1...)

If you want to find good formulas for prime numbers, go look it up in a good cryptology book. It should help better than any of us can.

Answer 2

As already mentioned, there are some advanced formulas for finding some large prime numbers. However for non-mathematical people, it's relatively quick and easy... Say you want to find all the prime numbers under 1,000... If you have a list of the numbers from 1 to 1000, you circle all the primes you know and cross off multiples of those primes. So, you'd cross off i, circle 2, and then cross off every multiple of 2! You're already half way through the list! Next,, circle 3 and cross any multiples of 3 you haven't crossed off yet. Keep it going until you know the rest of the numbers are prime. Not too hard. Takes some effort, but pretty easy.

Answer 3

you mean how to break a number down into the products of just prime numbers? you make a tree...like if the number is 18, 6 times 3 equals 18. 3 is already prime so u work on 6. 3 times 2 is 6 so now all your numbers are prime.

Answer 4

there is no direct formula but you can check if a number is prime or not if in a short way
a number A is said to be prime if
A mode n !=0 for every n
where n is any prime number less than square root of A
you can calculate prime numbers using MS Excel
you can e-mail me for more explaination!!

Answer 5

The three posts above are misinformed. There are direct formulas, although the ones plzselectano... gives are wrong. Here's a fair-sized list:
http://mathworld.wolfram.com/PrimeFormulas.html

In general, though, there are better ways than using these formulae. Here's another link:
http://mathworld.wolfram.com/PrimalityTest.html


In response to gjmb1960 below: Only the first formula on the page uses Mills' constant; there are many formulas there that can be computed quite directly. There are at least six others on the page I noted. For more information, see NJA Sloan's page on the primes, his sequence A000040:
http://www.research.att.com/~njas/sequences/A000040

Answer 6

There are methods to check if a given number "n"is prime Just check if n is divisible by integers from 2 to integral part of (n/2). If it is divisible by atleast one number in the range n is not prime, otherwise it is prime.

There are some formulae to generate prime numbers

see the following links

http://en.wikipedia.org/wiki/Formulas_for_prime_numbers

http://en.wikipedia.org/wiki/List_of_Prime_Numbers

Answer 7

There are many ways to find prime numbers. The best ones require some extremely advanced knowledge of mathematics.

Answer 8

There aint a direct formula.
Defn of prime number is: Any number, >1, which is divisible by itself and 1, only.

Answer 9

it is very simple... to find out a number is prime or not ....
for example take 13, make it a half i.e 13/2=6.5.......
now u have to do is divide 13 by 2,3,4,5,6 and check whether its divisible by any of the 2,3,4,5,6...... but 13 is not divisible by anyone...so 13 is a prime number.......


this concept is easy to write programs to find prime

Answer 10

there isnt any formula, many mathematicians hav been trying to find such formulas..There do exists some emperical formulas like that; eg 2^(2^n)+1 and 2^(2^n)-1 (plz check)