# Thread: Prime Test

1. ## Prime Test

I have a question for you guys.

I've attached an excel document with "Quick's Prime Test"

The question is, how often (excluding 2, 3, and 5) does it mess up?

If you can't read excel then I'll put tell you how it works...

2. Originally Posted by Quick

If you can't read excel then I'll put tell you how it works...
I cannot read it.

First, you should call it,
"Quick's Primality Algorithm" it sounds way cooler.

3. Originally Posted by ThePerfectHacker
I cannot read it.

First, you should call it,
"Quick's Primality Algorithm" it sounds way cooler.
Alright

Anyway "Quick's Primality Algorithm" works in 6 steps ($\displaystyle n$ is the # being tested).

1. is $\displaystyle n\div 11$ a whole #? (if yes, it's not prime. If no, go on)

2. is $\displaystyle n\div 5$ a whole #? (if yes, it's not prime. If no, go on)

3. is $\displaystyle (n-1)\div 4$ a whole #? (if yes, go to step 5. If no, go to step 4)

4. is $\displaystyle (n-3)\div 4$ a whole #? (if yes, go to step 5. If no, it's not prime)

5. is $\displaystyle (n-1)\div 6$ a whole #? (if yes, it's prime. If no, go to step 6)

6. is $\displaystyle (n-5)\div 6$ a whole #? (if yes, it's prime. If no, it's not prime)

4. I'm actually more interested to see if there is even a way to find out the ratio between actual primes and pseudoprimes for this test...

5. Originally Posted by Quick
I'm actually more interested to see if there is even a way to find out the ratio between actual primes and pseudoprimes for this test...
How did you develop this algorithm? as for your current signature, "Quick's Property: $\displaystyle \frac{n^2}{n-1}\div n=\frac{n^2}{n-1}-n$" what's that about? does it also have to do with primes?

6. Originally Posted by Jhevon
How did you develop this algorithm? as for your current signature, "Quick's Property: $\displaystyle \frac{n^2}{n-1}\div n=\frac{n^2}{n-1}-n$" what's that about? does it also have to do with primes?
I am the one who told him it does not work for 0 nor 1.

No, the signature is his own invention that he finds amusing that division gives the same result as subtraction.

7. Originally Posted by ThePerfectHacker
I am the one who told him it does not work for 0 nor 1.
He should just put a semi-colon between the 0 and the 1. It looks like 0,1 at the moment.

8. Originally Posted by janvdl
He should just put a semi-colon between the 0 and the 1. It looks like 0,1 at the moment.
The comma is the correct punctuation mark (not only that but in the US and
UK at least "." is the decimal point not "," so to our minds there is no
confusion.

RonL

9. Originally Posted by CaptainBlack
The comma is the correct punctuation mark (not only that but in the US and
UK at least "." is the decimal point not "," so to our minds there is no
confusion.

RonL
But South Africa adopted the British system many years ago.
And we use commas...