I know what a prime number is ( A number only divisible by itself or 1) I want to know if there is an easy formula to work out Prime Numbers when they get into the hundreds and thousands etc . Otherwise I could sit here for years ? lol.
2007-07-05 17:24:55 · 12 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
Yeah, u could there for years lol. But thanx to the internet, theres an easier way. http://math.about.com/library/blprimenumber.htm
2007-07-05 17:33:25 · answer #1 · answered by joe m 2 · 0⤊ 0⤋
I think you have started looking on a complicated problem.
1 2 3 5 7 11 13 17 19 23 29 31 37 39 41 43 47 53 59----------
are prime numbers.
I think you can give the computer this job if you really want to discover lots of them.
It is some interesting system of some of the numbers. May be about 20 % of the numbers are prime numbers. When we know that there are an unlimitede amont of numbers, we can conclude with the fact that we also have unlimited amount of prime numbers also.
2007-07-06 02:01:07 · answer #2 · answered by anordtug 6 · 1⤊ 0⤋
In fact, there is no pattern. The numbers roughly follow a known distribution, but there is no simple formula for generating the Nth prime number.
A bad way to test if a number is prime is to try dividing it by all numbers less than or equal to the square root of the number. If any of them divide evenly, the number isn't prime. This is incredibly slow for large numbers.
A good (fast) algorithm for testing whether or not a number is prime is the Miller-Rabin test. It runs very quickly, and only about 1/4 of composite numbers pass each test. So, if you do 20 Miller-Rabin tests on your number, and it passes all 20 tests, it will be reported as prime. The probability that it's actually composite is (1/4)^20.
2007-07-06 00:35:35 · answer #3 · answered by lithiumdeuteride 7 · 4⤊ 0⤋
what you need to do is know the divisibility tests for basic numbers.
For instance:
2: all even are out
3: add the numbers together, if it becomes a 3 6 or 9, out
5: ends in a 5 or a 0, out
7, divide it
if you cant find factors, then divide it by known primes up to half of the number. if that doesnt work, it is a prime number.
here is an arbitrary "big" number
603
if i add the numbers together, it is 9, not prime
2007-07-06 00:47:21 · answer #4 · answered by Anonymous · 0⤊ 2⤋
An ancient way is to use the Sieve of Aristophanes (?), ie starting with 2, divide by the previous un-struck positive integers, if evenly divisible at some point, strike it and go to the next integer and continue the process as far as desired.
The unstruck integers are prime.
2007-07-06 00:41:09 · answer #5 · answered by fjblume2000 2 · 2⤊ 0⤋
Even numbers above 2 are not prime numbers.
Rule of 3, 6, 9.
Rule of 0 and 5.
2007-07-06 00:42:14 · answer #6 · answered by Devon 6 · 0⤊ 2⤋
People have to use supercomputers to figure out prime number with loads of digits, so there's not an easy formula or anything like that. When they start to get higher up in digits, you just have to trial-and-error it, for the most part.
2007-07-06 00:28:47 · answer #7 · answered by quepie 6 · 2⤊ 0⤋
1. learn ur prime numbers till 200
2. learn divisibily tests.
eg:
for 2 - the number end in 0,2,4,6,8
for 5 -the number ends in 0, 5
3. learn ur tables till 30.
In the olden days, in India, people used to recite their tables after coming home from play... i learnt this in my marathi textbook
2007-07-06 04:46:51 · answer #8 · answered by Sean 3 · 0⤊ 1⤋
If the number is not divisible by any number smaller than itself.
2007-07-06 00:44:37 · answer #9 · answered by Snoopy 3 · 0⤊ 2⤋
Formula is known as Erasthones sieve, try googling
2007-07-06 03:48:23 · answer #10 · answered by Kathy S 5 · 0⤊ 2⤋