Friendly Numbers

[bigdaddyHess]

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

[Tony]

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)

[Prince]

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

[bigdaddyHess]

thnx tony
your answer is ownage