finish 15

src/euler15/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "euler15"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+rust-gmp = "*"
+
+[profile.release]
+lto = true

src/euler15/src/main.rs

@@ -0,0 +1,21 @@
+use gmp::mpz::Mpz;
+
+const LENGTH: usize = 20;
+fn main() {
+    for i in 1..=LENGTH {
+        let i = Mpz::from(i as u32);
+        print!("{i} x {i}: ");
+
+        let divisor = faculty(i.clone());
+        let result = faculty(Mpz::from(2) * i) / (divisor.clone() * divisor);
+        println!("{}", result);
+    }
+}
+
+fn faculty(x: Mpz) -> Mpz {
+    if x == Mpz::one() {
+        x
+    } else {
+        x.clone() * faculty(x - 1)
+    }
+}