diff --git a/plonky2/examples/duplex_testvector.rs b/plonky2/examples/duplex_testvector.rs
new file mode 100644
index 00000000..c33ca4cd
--- /dev/null
+++ b/plonky2/examples/duplex_testvector.rs
@@ -0,0 +1,40 @@
+use plonky2::field::types::Field;
+use plonky2::iop::challenger::*;
+use plonky2::hash::hashing::*;
+use plonky2::hash::poseidon::{PoseidonHash,Poseidon};
+use plonky2::plonk::config::{GenericConfig, PoseidonGoldilocksConfig};
+
+/// An example of using Plonky2 to prove a statement of the form
+/// "I know n * (n + 1) * ... * (n + 99)".
+/// When n == 1, this is proving knowledge of 100!.
+fn main() {
+    const D: usize = 2;
+    type C = PoseidonGoldilocksConfig;
+    type F = <C as GenericConfig<D>>::F;
+    type H =  PoseidonHash;
+
+    let mut duplex : Challenger<F,H> = Challenger::new();
+
+    let mut counter = 1001;
+    let mut sum: F = F::ZERO;
+    println!("duplexTestVector =");
+    let mut c = '[';
+    for a in 1..21 {
+        for s in 1..21 {
+            for i in 0..a { 
+                duplex.observe_element(F::from_canonical_u64(counter));
+                counter = counter+1;
+            }
+            println!("    -- #absorb = {} -> #squeeze = {}",a,s);
+            for i in 0..s { 
+                let out = duplex.get_challenge();
+                sum = sum + out;
+                println!("  {} {}",c,out);
+                c = ',';
+            }
+        }
+    }
+    println!("  ]");
+    println!("");
+    println!("sum = {}",sum);
+}