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MathNet 2025 — 50 problems with figures (EN–VI) Question 1

Math Olympiad Vault · MathNet 2025 — 50 problems with figures (EN–VI)

Question 1

The 27 cells of a $3 \times 9$ grid are filled in using the numbers 1 through 9 so that each row contains 9 different numbers, and each of the three $3 \times 3$ blocks heavily outlined in the example below contains 9 different numbers, as in the first three rows of a Sudoku puzzle.

Question illustration

The number of different ways to fill such a grid can be written as $p^a \cdot q^b \cdot r^c \cdot s^d$, where $p, q, r$, and $s$ are distinct prime numbers and $a, b, c$, and $d$ are positive integers. Find $p \cdot a + q \cdot b + r \cdot c + s \cdot d$.