diff --git a/Cargo.lock b/Cargo.lock
index 1ea8b8e..db4a39b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2724,6 +2724,10 @@ version = "1.70.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8478577c03552c21db0e2724ffb8986a5ce7af88107e6be5d2ee6e158c12800"
 
+[[package]]
+name = "iter-prod"
+version = "0.1.0"
+
 [[package]]
 name = "itertools"
 version = "0.10.5"
diff --git a/Cargo.toml b/Cargo.toml
index 0b03032..2e3fc13 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -30,9 +30,11 @@ members = [
   "members/arithmetics",
   "members/egui-demo",
   "members/rfd-demo",
+  "members/iter-prod",
 ]
 default-members = [
   ".",
+  "members/iter-prod",
   "members/rfd-demo",
   "members/egui-demo",
   "members/arithmetics",
diff --git a/members/iter-prod/Cargo.toml b/members/iter-prod/Cargo.toml
new file mode 100644
index 0000000..366207d
--- /dev/null
+++ b/members/iter-prod/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "iter-prod"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/members/iter-prod/src/main.rs b/members/iter-prod/src/main.rs
new file mode 100644
index 0000000..c4e25e9
--- /dev/null
+++ b/members/iter-prod/src/main.rs
@@ -0,0 +1,35 @@
+fn main() {
+    let x = 7;
+    println!("{}", factorial(x));
+}
+
+fn factorial(n: u128) -> u128 {
+    (1..n + 1).product()
+}
+
+// does the same as product from the stdlib
+#[allow(dead_code)]
+fn myprod<T>(iter: T) -> u128
+where
+    T: Iterator<Item = u128>,
+{
+    #[allow(clippy::unnecessary_fold)] // clippy detects that this is just Iter::product
+    iter.fold(1, |acc, v| acc * v)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn works() {
+        assert_eq!(factorial(7), 5040);
+        assert_eq!(factorial(9), 362880);
+    }
+
+    #[test]
+    fn myprod_same_as_real() {
+        assert_eq!((1..5).product::<u128>(), myprod(1..5));
+        assert_eq!((1..30).product::<u128>(), myprod(1..30));
+        // assert_eq!((1..50).product::<u128>(), myprod(1..50)); // u128 overflows here
+    }
+}