diff --git a/p11.c b/p11.c
index 88ed54b..9f27085 100644
--- a/p11.c
+++ b/p11.c
@@ -18,15 +18,15 @@
 #define prd(x, y) (grid[y][x] * grid[y-1][x+1] * grid[y-2][x+2] * grid[y-3][x+3])
 
 /* macro for checking all directions of a square x,y */
-#define check_square(x, y) \
-    do { \
-        if (x < 17) \
-            setprod(px(x, y)); \
-        if (y < 17) \
-            setprod(py(x, y)); \
-        if (x < 17 && y < 17) \
-            setprod(pd(x, y)); \
-        if (x >= 3 && y >= 3) \
+#define check_square(x, y)      \
+    do {                        \
+        if (x < 17)             \
+            setprod(px(x, y));  \
+        if (y < 17)             \
+            setprod(py(x, y));  \
+        if (x < 17 && y < 17)   \
+            setprod(pd(x, y));  \
+        if (x >= 3 && y >= 3)   \
             setprod(prd(x, y)); \
     } while(0)
 
diff --git a/p20.c b/p20.c
new file mode 100644
index 0000000..21f2d4f
--- /dev/null
+++ b/p20.c
@@ -0,0 +1,46 @@
+
+/*
+ * http://projecteuler.net
+ * 
+ * Projecteuler - Problem 20
+ * ------------------------
+ * 2010-05-17 Henrik Hautakoski
+ *
+ * easy with a good lib for doing arbitrary-precision arithmetic
+ */
+
+#include <stdio.h>
+#include <malloc.h>
+#include <gmp.h>
+
+char* fak(int n) {
+
+    mpz_t v;
+    mpz_init(v);
+    mpz_fac_ui(v, n);
+    return mpz_get_str(NULL, 10, v);
+}
+
+int sum(char *n) {
+    
+    int num = 0;
+    
+    for(; *n != '\0'; n++)
+        num += (*n) - 0x30;
+        
+    return num;
+}
+
+int main() {
+
+    char *n = fak(100);
+
+    if (n == NULL)
+        return 1;
+
+    printf("%i\n", sum(n));
+
+    free(n);
+
+    return 0;
+}