9x9

9x9, pronounced "nine by nine," denotes a two-dimensional grid that has nine units along each of its two axes. In other words, it is a square array of 81 cells arranged in nine rows and nine columns. The term is used across mathematics, puzzles, games, and digital contexts to describe the dimensions of a grid, matrix, or image.

In arithmetic, 9 × 9 equals 81. The number 81 is a perfect square (9 squared) and equals 3^4, illustrating its standing as a power of a single integer.

One of the most common references to 9x9 is the Sudoku puzzle, which uses a 9×9 grid subdivided into nine 3×3 subgrids. The goal is to fill the grid so that each row, column, and subgrid contains all digits from 1 to 9 exactly once.

9x9 boards are also used in the game of Go as a smaller variant, offering shorter games and simplified strategy compared to the standard 19x19 board. While not the universal standard for Go, the 9x9 format is widely supported for teaching, experimentation, and fast play.

In mathematics and computing, a 9x9 matrix is a square matrix with 81 entries. Such matrices appear in various applications, including numerical simulations, image processing, and solving systems of linear equations. The concept generalizes to grids of other sizes as well.