Computer Science Canada

Friendly Numbers
Author:  bigdaddyHess [ Wed Apr 09, 2003 2:45 pm ]
Post subject:  Friendly Numbers
how can i print a list of friendly numbers (up to 20000 btw)?

two numbers are friendly is the sum of factors of one is equal to the other number

for eg. 220 & 284

sum of factors of 220 is equal to 284
and sum of factors of 284 is equal to 220
Author:  Tony [ Wed Apr 09, 2003 2:51 pm ]
Post subject: 
the simpliest way I can think of is start finding sums of factors of the first number. Then take the sum, add up its factors and see if it equals to original number or not.

code:

for i:1..20000

sum:=sumoffactors(i) %sumoffactors is an outside function

sum2:=sumoffactiors(sum)

if sum2 = i then
put i, " and ", sum, " are friendly numbers"
end if

end for


all thats left is writing a function to addup the factors. I actually think someone already posted it somewhere on this board. (try using search feature)
Author:  Prince [ Wed Apr 09, 2003 5:58 pm ]
Post subject: 
code:

function properFactors (n : int) : int
    var x, y, temp : int := 0
    for decreasing i : n .. 1 by 1
        x := n mod i
        if x = 0 then
            y := n div i
            if y not= n then
                temp := temp + y
            end if
        end if
    end for
    result temp
end properFactors


no searching involved
Author:  bigdaddyHess [ Thu Apr 10, 2003 2:06 pm ]
Post subject:  thnx
thnx tony
your answer is ownage

:


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