add more help text

cmd/mobius.go

@@ -73,10 +73,16 @@ func mobius(cmd *cobra.Command, args []string) {
 
 // mobiusCmd represents the mobius command
 var mobiusCmd = &cobra.Command{
-	Use:   "mobius",
+	Use:   "mobius -n N",
 	Short: "Compute the Möbius function for all numbers less than n",
-	Long:  `Compute the Möbius function for all numbers less than n.`,
-	Run:   mobius,
+	Long: `Compute the Möbius function for all numbers less than n.
+
+The Möbius function mu(n) is a multiplicative function defined as follows for prime p:
+mu(p) = -1
+mu(p^k) = 0 for k > 1
+
+This means for squarefree n, mu(n) = -1 if n has an odd number of prime factors and mu(n) = 1 if n has an even number of prime factors. mu(n) = 0 if n is not squarefree.`,
+	Run: mobius,
 }
 
 func init() {