diff --git a/math/math.v b/math/math.v
index d5e9c6745e..7d071a037d 100644
--- a/math/math.v
+++ b/math/math.v
@@ -8,6 +8,7 @@ const (
 	E   = 2.71828182845904523536028747135266249775724709369995957496696763
 	Pi  = 3.14159265358979323846264338327950288419716939937510582097494459
 	Phi = 1.61803398874989484820458683436563811772030917980576286213544862
+	Tau = 6.28318530717958647692528676655900576839433879875021164194988918
 
 	Sqrt2   = 1.41421356237309504880168872420969807856967187537694807317667974
 	SqrtE   = 1.64872127070012814684865078781416357165377610071014801157507931
@@ -128,3 +129,12 @@ pub fn tanh(a f64) f64 {
 pub fn trunc(a f64) f64 {
 	return C.trunc(a)
 }
+
+pub fn factorial(a int) i64 {
+	mut prod := 1	
+	for i:= 0; i < a; i++ {
+		prod = prod * (i+1)
+	}
+	return prod
+}
+