diff --git a/src/is_prime.rs b/src/is_prime.rs
index a509379..4a201d3 100644
--- a/src/is_prime.rs
+++ b/src/is_prime.rs
@@ -1,5 +1,6 @@
 pub mod prime_utils {
     use num::{BigUint, One};
+    use once_cell::sync::Lazy;
 
     #[must_use]
     pub fn log_2(x: &BigUint) -> u64 {
@@ -8,32 +9,31 @@ pub mod prime_utils {
 
     #[must_use]
     pub fn is_prime(number: &BigUint) -> bool {
-        if BigUint::one() == *number {
+        const ZERO: BigUint = BigUint::ZERO;
+        static TWO: Lazy<BigUint> = Lazy::new(|| BigUint::from(2u8));
+
+        if &BigUint::one() >= number {
             return false;
         }
-        if BigUint::from(4u8) > *number {
+        if &BigUint::from(4u8) > number {
             return true;
         }
+        if number % &*TWO == ZERO {
+            return false;
+        }
 
         // number = 2^a - 1
         // a = log2(number + 1)
         let a = log_2(&(number + 1u8));
 
         //if number isn't a mersenne number
-        if BigUint::from(2u8).pow(a as u32) - BigUint::one() != *number {
-            const ZERO: BigUint = BigUint::ZERO;
+        if TWO.pow(a as u32) - BigUint::one() != *number {
             let mut i = BigUint::one();
-            let one = BigUint::one();
-            let two = &one + &one;
 
-            if number % &two == ZERO {
-                return false;
-            }
-
-            let sqrtnum = number.sqrt() + one; //fake ceil function
+            let sqrtnum = number.sqrt() + BigUint::one(); //fake ceil function
 
             loop {
-                i += &two; //we begin checking 3 and then continue with every second number as every even number is divisible by 2 and we already checked that
+                i += &*TWO; //we begin checking 3 and then continue with every second number as every even number is divisible by 2 and we already checked that
                 if number % &i == ZERO {
                     return false;
                 }
@@ -44,14 +44,12 @@ pub mod prime_utils {
         }
 
         //check if it's a mersenne prime
-        // 4 12 194
         let mut last = BigUint::from(4u8);
-        let two = BigUint::from(2u8);
 
         for _i in 2..a {
-            last = (last.pow(2) - &two) % number;
+            last = (last.pow(2) - &*TWO) % number;
         }
 
-        last == BigUint::from(0u8)
+        last == BigUint::ZERO
     }
 }
diff --git a/src/main.rs b/src/main.rs
index 105345c..3aa3eb2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -12,7 +12,7 @@ use std::{
     io::Write,
     sync::{
         atomic::{AtomicU64, AtomicUsize},
-        Arc, RwLock,
+        Arc, Mutex,
     },
     thread,
     time::SystemTime,
@@ -67,7 +67,7 @@ fn worker(
     workloads: usize,
     i: usize,
     progress: &AtomicU64,
-    arcclone: &Arc<RwLock<Vec<BigUint>>>,
+    arcclone: &Arc<Mutex<Vec<BigUint>>>,
     threads_done: &AtomicUsize,
 ) {
     #[cfg(target_os = "windows")]
@@ -90,7 +90,7 @@ fn worker(
         }
     }
 
-    arcclone.write().unwrap().append(&mut primecache);
+    arcclone.lock().unwrap().append(&mut primecache);
 
     threads_done.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
 }
@@ -100,11 +100,11 @@ fn main() {
     if args.len() == 2 {
         use std::str::FromStr;
         let prime = args.nth(1).unwrap();
+        let prime = BigUint::from_str(&prime).unwrap();
 
-        println!(
-            "Number is prime: {}",
-            is_prime::prime_utils::is_prime(&BigUint::from_str(&prime).unwrap())
-        );
+        let is_prime = is_prime::prime_utils::is_prime(&prime);
+
+        println!("Number is {}a prime", if is_prime { "" } else { "not " });
 
         return;
     }
@@ -116,7 +116,7 @@ fn main() {
     let workloads = nthprime_approx / THREADS;
 
     let primecache: Vec<BigUint> = Vec::with_capacity(NU);
-    let primemutex = std::sync::RwLock::new(primecache);
+    let primemutex = std::sync::Mutex::new(primecache);
     let primearc = std::sync::Arc::new(primemutex);
 
     let progress_val = AtomicU64::new(0);
@@ -136,11 +136,13 @@ fn main() {
             let threads_completed = threads_done.load(std::sync::atomic::Ordering::Relaxed);
 
             println!(
-                "Progress: {}/{} ({:.0}%) | {}",
+                "Progress: {:0>width$}/{} ({:>3}%) | {:0>t_width$}",
                 n,
                 N,
-                n as f64 / NF * 100.0,
-                threads_completed
+                (n as f64 / NF * 100.0).min(100.0).floor(),
+                threads_completed,
+                width = N.to_string().len(),
+                t_width = THREADS.to_string().len()
             );
             std::thread::sleep(std::time::Duration::from_millis(500));
 
@@ -150,7 +152,7 @@ fn main() {
         }
     });
 
-    let mut primes = primearc.write().unwrap();
+    let mut primes = primearc.lock().unwrap();
     primes.sort_unstable();
 
     #[allow(clippy::cast_possible_wrap)]