 /*
Let d(n) be defined as the sum of proper divisors of n (numbers less than n
which divide evenly into n). If d(a) = b and d(b) = a, where a ≠ b, then a and
b are an amicable pair and each of a and b are called amicable numbers.
For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55
and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and
142; so d(284) = 220.
Evaluate the sum of all the amicable numbers under 10000.
Answer: 31626
*/
package main
import "fmt"
func sumFactors(n int) int {
max := n/2 + 1
count := 0
for i := 1; i <= max; i++ {
if n%i == 0 {
count += i
}
}
return count
}
func main() {
seen := map[int]bool{}
for i := 1; i < 10000; i++ {
sf := sumFactors(i)
if sf != i && sumFactors(sf) == i {
seen[i] = true
}
}
sum := 0
for a := range seen {
sum += a
}
fmt.Println(sum)
}
