diff --git a/append_digit_primes/src/main.rs b/append_digit_primes/src/main.rs
index 604bd5c..d645554 100644
--- a/append_digit_primes/src/main.rs
+++ b/append_digit_primes/src/main.rs
@@ -16,14 +16,14 @@ impl Tree {
         }
     }
 
-    fn to_string(&self) -> String {
-        let mut retval = format!("[{}: ", self.value);
-        for child in &self.children {
-            retval.push_str(&child.to_string()[..]);
-        }
-        retval.push(']');
-        retval
-    }
+    // fn to_string(&self) -> String {
+    //     let mut retval = format!("[{}: ", self.value);
+    //     for child in &self.children {
+    //         retval.push_str(&child.to_string()[..]);
+    //     }
+    //     retval.push(']');
+    //     retval
+    // }
 
     fn step(&mut self) {
         if self.children.is_empty() {
@@ -70,11 +70,17 @@ fn step(x: u64) -> Vec<u64> {
 }
 
 fn main() {
-    let primes: Vec<u64> = primal::Primes::all().skip_while(|x| *x < 10_000_000).take_while(|x| *x < 100_000_000).map(|x| x as u64).collect();
+    /* find all non-truncatable primes in (100,000,000; 1,000,000,000) */
+    let primes: Vec<u64> = primal::Primes::all()
+        .skip_while(|x| *x < 100_000_000)
+        .take_while(|x| *x < 1_000_000_000)
+        .map(|x| x as u64)
+        .filter(|x| !(primal::is_prime(*x / 10)))
+        .collect();
+
     let mut tree = Tree::new(0, primes);
     for _ in 0..20 {
         tree.step();
         println!("{:?}", tree.longest_path());
     }
-    //println!("{}", tree.to_string());
 }