add more help text

cmd/divisors.go

@@ -103,10 +103,19 @@ func divisors(cmd *cobra.Command, args []string) {
 
 // divisorsCmd represents the divisors command
 var divisorsCmd = &cobra.Command{
-	Use:   "divisors",
+	Use:   "divisors -n N",
 	Short: "Compute the divisor function for all numbers less than n",
-	Long:  `Compute the divisor function for all numbers less than n.`,
-	Run:   divisors,
+	Long: `Compute the divisor function for all numbers less than n.
+
+sigma_x(n) computes the sum of the xth powers of the divisors of n.
+For example, the divisors of 12 are 1, 2, 3, 4, 6, and 12.
+sigma_0(12) = 6
+sigma_1(12) = 1 + 2 + 3 + 4 + 6 + 12 = 28
+sigma_2(12) = 1^2 + 2^2 + 3^2 + 4^2 + 6^2 + 12^2 = 210
+
+This program computes sigma for all values less than the input n.
+Provide the --exponent flag to set the desired exponent for each sum.`,
+	Run: divisors,
 }
 
 func init() {