package main

func sumdiv(j int) int {
sum := 1
for i := 2; i < j; i++ {
 if j%i == 0 {
  sum += i
 }
}
return sum
}

func main() {
sum := 0
cache := make(map[int]int)
for i := 1; i < 10000; i++ {
 j, ok := cache[i]
 if !ok {
  j = sumdiv(i)
  cache[i] = j
 }
 if i != j && i == sumdiv(j) {
  sum += i
 }
}
println(sum)
}

package main

import "sync"

func sumdiv(j int) int {
sum := 1
for i := 2; i < j; i++ {
 if j%i == 0 {
  sum += i
 }
}
return sum
}

func main() {
const MAX = 10000
cache := [MAX + 1]int{}
work := make(chan int, 100)
wg := sync.WaitGroup{}

dowork := func(w chan int) {
 for i := range w {
  j := sumdiv(i)
  cache[i] = j
 }
 wg.Done()
}

// Let's go, 8 cores!
for i := 0; i < 8; i++ {
 wg.Add(1)
 go dowork(work)
}
for i := 1; i < MAX; i++ {
 work <- i
}
close(work)
wg.Wait()
sum := 0
for i := 1; i < MAX; i++ {
 j := cache[i]
 if j > MAX {
  continue
 }
 if i != j && i == cache[j] {
  sum += i
 }
}
println(sum)
}

package main

func main() {
const MAX = 10000
cache := [MAX + 1]int{}
cache[1]++

// Construct sieve of eratosthenes
for i := 1; i <= MAX; i++ {
 for j := i + i; j <= MAX; j += i {
  cache[j] += i
 }
}

sum := 0
for i := 1; i < MAX; i++ {
 j := cache[i]
 if j <= MAX && i != j && i == cache[j] {
  sum += i
 }
}
println(sum)
}

angch@mondas code % cat golf.pl
for(1..1e4){for($i=$_*2;$i<=1e4;$i+=$_){$a[$i]+=$_}}
for(1..1e4){$b=$a[$_];$s+=$_ if$_==$a[$b]&&$_!=$b;}
print$s;                                                                                
angch@mondas code % perl golf.pl
31626%  

echo 31626