This is a book that, to our knowledge, has never before appeared in print: 163 killer sudoku puzzles in which every cage sum is a prime number. We believe this is the first commercially published collection of prime killer sudoku, and we chose the puzzle count of 163 deliberately � " 163 is a Heegner number, one of only nine integers with a celebrated connection to algebraic number theory and elliptic curves, and it is the largest value of d for which the number field Q(sqrt(-d)) has unique factorization. There is also the famous Ramanujan near-integer identity: e raised to (pi times the square root of 163) is within one part in a trillion of an integer, a coincidence so improbable that Ramanujan noticed it decades before anyone could explain why. For a book where every cage sum must itself be prime, a puzzle count drawn from the deep structure of number theory felt right. Prime killer sudoku adds a number-theoretic layer to an already demanding variant. In ordinary killer sudoku the cage sums can take any value from one to forty-five; in prime killer they are restricted to the primes below forty-five: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, and 43. Fourteen numbers, no others. The reader who wants to solve these puzzles efficiently does well to commit the admissible sums to memory before beginning, and to work through the two-cell and three-cell partitions of each prime. Two admits nothing in two cells of distinct digits. Three admits only 1 + 2. Five admits 1 + 4 or 2 + 3. Seven admits 1 + 6, 2 + 5, or 3 + 4. Eleven admits 2 + 9, 3 + 8, 4 + 7, and 5 + 6 in two cells, and 1 + 3 + 7, 1 + 4 + 6, 2 + 3 + 6, 2 + 4 + 5 in three cells. The combinatorial inventory grows quickly from there, and mastering it is half the satisfaction of the variant. The other technique that matters in prime killer is parity awareness. Because two is the only even prime, a cage summing to any other prime must have odd sum, which means its digit composition must satisfy specific parity constraints � " an odd count of odd digits. This lets you make early eliminations in cages where you cannot yet determine the exact digits. Combined with the classic Rule of 45 (each row, column, and box sums to forty-five), parity considerations turn prime killer into a variant where arithmetic reasoning is primary and positional reasoning is secondary. Every puzzle in this book was algorithmically generated and verified to have exactly one solution by an exhaustive backtracking solver, the same verification pipeline that powers every title in the Proven Puzzles line. The answer key includes a cryptographic SHA-256 hash under every grid so the puzzle� "solution pair can be independently checked. The Editor's Note is signed by our Euler AI persona � " an artificial mind trained upon the letters and treatises of Leonhard Euler (1707� "1783), speaking here in a modern English rendering of that voice. Prime numbers were a lifelong subject of Euler's correspondence; his note for this book discusses the arithmetic of the prime cage-sum universe with his characteristic combination of formal rigor and practical encouragement. The 163 puzzles range in difficulty from moderate to expert. The gentler entries introduce the prime-sum constraint one cage at a time; the harder puzzles exploit deep partition combinatorics to create solving chains of remarkable length. Solvers who enjoy ordinary killer sudoku will find prime killer a natural next step; solvers new to the variant should start from the front of the book and work forward. Contents: Publisher's Note, Euler AI's Editor's Note on the arithmetic of the prime cage-sum universe, rules page with a partition reference for every admissible prime, 163 verified puzzles, complete answer key with verification line per grid, verification methodology, and production notes. Typeset in Avenir Next on 70 lb bright white paper; perfect bound; 6 x 9 inches.
