4×4 Hard Mathdoku 4×4 Mathdoku Puzzles 4×4 Hard 10 puzzles available 🧩 4×4 Hard #1 B → 🧩 4×4 Hard #2 B → 🧩 4×4 Hard #3 B → 🧩 4×4 Hard #4 B → 🧩 4×4 Hard #5 B → 🧩 4×4 Hard #6 B → 🧩 4×4 Hard #7 B → 🧩 4×4 Hard #8 B → 🧩 4×4 Hard #9 B → 🧩 4×4 Hard #10 B →