Program to Determine Perfect Numbers

[CITC]

Unfortunately this program takes really long to determine the perfect numbers after 1700 something... I don't think theres any better way to do it though, or it hasn't been discovered yet.. this is brute force!!

for any who don't know: Perfect Numbers are numbers that their factors (excluding the number itself) add up to the number... wow explained that bad, here's an example.
6 is a perfect number.. factors of 6 = 1,2,3,6.. exclude 6... 1+2+3 = 6

code:

var num : int := 0 var key : string (1) loop    cls    num += 1    var keep : array 1 .. num of int    var total : int := 0    for k : 1 .. num        keep (k) := 0    end for    for i : 1 .. num        if num rem i = 0 then            keep (i) := i        end if    end for    for p : 1 .. num        if keep (p) not= 0 then            total += keep (p)        end if    end for    if (total div num = 2) and (total rem num = 0) then        put num        for o : 1 .. num            if keep (o) not= 0 then                put keep (o), ", " ..            end if        end for        getch (key)    end if end loop

[McKenzie]

A bit faster:

code:

function isPerfect (n : int) : boolean     var sum := 0     for i : 1 .. n div 2         if n mod i = 0 then             sum := sum + i         end if     end for     if sum = n then         result true     else         result false     end if end isPerfect var now:int for i:1..10000     if isPerfect(i) then         put i        clock(now)        put "time ",now/1000 :0:2, " Seconds"        end if end for

The timer stuff is there because I was comparing with yours to make sure mine was worth posting.

[AsianSensation]

CITC wrote:

I don't think theres any better way to do it though, or it hasn't been discovered yet..

yeah, actually there is a better way, there is a formula that let you derive any perfect number, google it up, I sure it's on the web somewhere.

or you can prove it yourself?

[Andy]

LOL.... formulas... the reason why we use compsci is cuz we dont like formulas.... its actually the same speed for a computer to use a for loop to add one to a number than to multiply the number

[CITC]

Your right there is a formula for it. I'll post the program in a day or two probably.

[santabruzer]

i've always wondered if there was a formula for prime numbers.. so that you wouldn't have to devide by every number halfway up to that number... and for perfect ones.. iyea.. it's cool.. there's a formula...

[AsianSensation]

there is no formula for prime numbers, that's why really really large prime numbers are used to encrypt many many things.

[Andy]

but u can get a program that generates prime numbers... me and shaun are making one, one of these days

[AsianSensation]

sure, there are many many ways of generating a prime number, but starting with the Mersenne (did I spell that right?) prime is what they do now to find a really large prime number. Mersenne primes are number in the form of 2^n - 1. The other day, we were told that the largest prime known was updated again, and they found that number by passing parts of the prime finding program to alot of computers, so if you want to be part of the finding team, all you have to do was download their program, and it runs in the background. Then they take all the info generated at different computer and come up with the number.

[CITC]

I heard about 1 year and a half ago (i think) that an Indian mathemetician who was amazing with numbers and patterns had discovered a formula to get prime numbers... read it in some magazine, dunno which. I'm not too sure though, I could be wrong.

btw, that bit about the mersenne prime formula being 2^n - 1 is half of the perfect number formula.

its 2^(n - 1) * (2^n - 1)

I'm overwhelmed with trying to get the slime volleyball bouncing thing working though, if no one else makes this program and posts it, I'll make it when I can.

Cheers