Added 3n+1

Maths/3n+1.py

@@ -0,0 +1,14 @@
+def n31(a):# a = initial number
+    c = 0
+    l = [a]
+    while a != 1:
+        if a % 2 == 0:#if even divide it by 2
+            a = a // 2
+        elif a % 2 == 1:#if odd 3n+1
+            a = 3*a +1
+        c += 1#counter
+        l += [a]
+        print(a)#optional print
+    print("It took {0} steps.".format(c))#optional finish
+    return l , c
+print(n31(43))