diff --git a/rust/fourthfree/Cargo.toml b/rust/fourthfree/Cargo.toml
new file mode 100644
index 0000000..ed6ff3b
--- /dev/null
+++ b/rust/fourthfree/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "fourthfree"
+version = "0.1.0"
+authors = ["William Ball <wball1@swarthmore.edu>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+rug = "1.10.0"
diff --git a/rust/fourthfree/src/main.rs b/rust/fourthfree/src/main.rs
new file mode 100644
index 0000000..30790ac
--- /dev/null
+++ b/rust/fourthfree/src/main.rs
@@ -0,0 +1,79 @@
+use rug::{Assign, Integer};
+use std::thread;
+
+const NUM_THREADS: usize = 12;
+const BASE: u64 = 10;
+
+fn is_fourth_free(x: &Integer) -> bool {
+    let mut i = Integer::new();
+    i.assign(2);
+    let mut fourth = Integer::from(&Integer::from(&i * &i) * &Integer::from(&i * &i));
+    while fourth < *x {
+        if x % (fourth) == 0 {
+            return false;
+        }
+        i += 1;
+        fourth = Integer::from(&Integer::from(&i * &i) * &Integer::from(&i * &i));
+    }
+    true
+}
+
+fn step(x: &Integer) -> Vec<Integer> {
+    let mut new_xs = Vec::new();
+    for d in 0..BASE {
+        let mut temp = Integer::from(x * BASE);
+        temp += d;
+        if is_fourth_free(&temp) {
+            new_xs.push(temp);
+        }
+    }
+    new_xs
+}
+
+fn next(ls: &Vec<Integer>) -> Vec<Integer> {
+    let mut new: Vec<Integer> = Vec::new();
+    let mut slices: Vec<Vec<Integer>> = Vec::new();
+    let mut children = Vec::with_capacity(NUM_THREADS);
+    let size = ls.len() / NUM_THREADS;
+    for i in 0..(NUM_THREADS - 1) {
+        let mut new = Vec::with_capacity(size);
+        for val in ls.iter().skip(size * i).take(size) {
+            new.push(val.clone());
+        }
+        slices.push(new);
+    }
+    {
+        let mut new = Vec::new();
+        for val in ls.iter().skip(size * (NUM_THREADS - 1)) {
+            new.push(val.clone());
+        }
+        slices.push(new);
+    }
+    for slice in slices {
+        children.push(thread::spawn(move || -> Vec<Integer> {
+            let mut new = Vec::new();
+            for oldval in slice {
+                new.append(&mut step(&oldval));
+            }
+            new
+        }));
+    }
+    for child in children {
+        new.append(&mut child.join().unwrap());
+    }
+    new
+}
+
+fn main() {
+    let mut i = 0;
+    let mut ls: Vec<Integer> = (1..BASE)
+        .into_iter()
+        .map(|x| Integer::from(x))
+        .filter(|x| is_fourth_free(x))
+        .collect();
+    loop {
+        i += 1;
+        println!("{}\t{}", i, ls.len());
+        ls = next(&ls);
+    }
+}
diff --git a/rust/insert_digit_anywhere_primes_constant/log b/rust/insert_digit_anywhere_primes_constant/log
new file mode 100644
index 0000000..2c2539c
--- /dev/null
+++ b/rust/insert_digit_anywhere_primes_constant/log
@@ -0,0 +1,9 @@
+6	1.3815510557964277
+7.675	1.7672340588729303
+8.657602339181286	1.9934866087269214
+9.287908478277238	2.1386199607174183
+9.706992706401598	2.235117670356225
+10.021722699613848	2.3075869294250895
+10.26388157204211	2.3633460704040457
+10.456005647430802	2.407584273603572
+10.613201775385221	2.4437800196939956
diff --git a/rust/insert_digit_anywhere_primes_constant/src/main.rs b/rust/insert_digit_anywhere_primes_constant/src/main.rs
index 5405e5a..a782762 100644
--- a/rust/insert_digit_anywhere_primes_constant/src/main.rs
+++ b/rust/insert_digit_anywhere_primes_constant/src/main.rs
@@ -2,8 +2,8 @@ use std::thread;
 use std::collections::HashSet;
 
 const NUM_THREADS: usize = 6;
-const THREAD_SKIP: u64 = 1_000;
-const BASE: u64 = 16;
+// const THREAD_SKIP: u64 = 1_000;
+const BASE: u64 = 10;
 
 fn remove_duplicates(ls: Vec<u64>) -> Vec<u64> {
     let mut hs: HashSet<u64> = HashSet::new();
@@ -82,11 +82,11 @@ fn next(ls: Vec<u64>) -> (f64, Vec<u64>) {
             let mut new = Vec::new();
             let mut count = 0;
             for oldval in slice {
-                // let mut temp = step(oldval);
-                let temp = step(oldval);
+                let mut temp = step(oldval);
+                // let temp = step(oldval);
                 count += temp.len() as u64;
-                new.push(oldval + THREAD_SKIP);
-                // new.append(&mut temp);
+                // new.push(oldval + THREAD_SKIP);
+                new.append(&mut temp);
             }
             (count, new)
         }));
@@ -100,13 +100,13 @@ fn next(ls: Vec<u64>) -> (f64, Vec<u64>) {
 }
 
 fn main() {
-    let mut ls: Vec<u64> = (1..(NUM_THREADS as u64) * THREAD_SKIP)
-        .into_iter()
-        .collect();
+    // let mut ls: Vec<u64> = (1..(NUM_THREADS as u64) * THREAD_SKIP)
+    //     .into_iter()
+    //     .collect();
     let mut count: f64;
     let mut i = 0;
     let mut total: f64 = 0.0;
-    // let mut ls = primal::Primes::all().take_while(|x| *x < BASE as usize).map(|x| x as u64).collect();
+    let mut ls = primal::Primes::all().take_while(|x| *x < BASE as usize).map(|x| x as u64).collect();
     loop {
         let res = next(ls);
         count = res.0;