Crossnumber

Crossnumber is a puzzle in which a grid is filled with digits to form across and down entries, each matching a clue that describes a number or numerical property. It is the numerical counterpart of the crossword puzzle, with the goal of placing digits so that every across and down entry satisfies its clue.

The grid resembles a crossword grid, with white cells forming across and down entries separated by black squares. Each entry runs through consecutive white cells and is assigned a clue. Clues are typically given for across and down entries, and the digits in an entry form a legitimate number or arithmetic expression, depending on the clue. Common conventions include no leading zeros and consistent numbering of clues. Clues may be straightforward definitions of numbers (for example, “the smallest prime”), descriptions of numerical properties (such as “the sum of the digits is 15”), or references to arithmetic operations and sequences.

Crossnumbers originated in puzzle magazines in the early 20th century and have since appeared in newspapers, books, and online puzzles. Solving a crossnumber combines numerical knowledge, logical deduction, arithmetic skills, and pattern recognition; solvers often check cross-checked digits against intersecting entries to ensure compatibility.

Related puzzles include crosswords and Kakuro; like crosswords, crossnumbers come in various themes and difficulty levels and can be published with varying conventions. Variants exist, including larger grids, themed clues, and alternative clue formats, but the core idea remains filling a grid with digits to satisfy all clues.