1 files changed, 35 insertions, 0 deletions
diff --git a/021.c b/021.c
new file mode 100644
index 0000000..e236cf3
--- /dev/null
+++ b/021.c
@@ -0,0 +1,35 @@
+#include <math.h>
+
+int sum_divisors(int number)
+{
+	int i;
+	int sum = 1;
+	int limit = (int) ceil(sqrt(number));
+	for(i=2; i<limit; i++)
+	{
+		if(number % i == 0)
+		{
+			sum += i;
+			if(number / i != i)
+				sum += number / i;
+		}
+	}
+	return sum;
+}
+
+int main()
+{
+	int sum = 0;
+	int a;
+	for(a=1; a<10000; a++)
+	{
+		int b = sum_divisors(a);
+		if(a == sum_divisors(b) && a != b)
+			sum += a;
+	}
+
+	printf("%d\n", sum);
+
+	return 0;
+}
+