Math in English and Puzzles and Brains both contain printable Numbrix-like puzzles for free. Although they are not official Numbrix puzzles, the goal of the crossword-like number puzzles is the same as the original game. Printable puzzles are as small as a 3-by-3 game up to a 15-by-15 puzzle. Smaller puzzles are easier to accomplish, and larger grids are more difficult.
The point of Numbrix is to fill in a grid of numbers so each one is connected in ascending order. The official game is a 9-by-9 grid of numbers from 1 to 81. There is no math, arithmetic or special trick to figure out the pattern of numbers. The key is to reason, with logic, what numbers are adjacent to others. The only rule is that progressively larger numbers are inserted vertically or horizontally, not diagonally. The puzzle is complete when a player can draw a continuous line from the lowest number to the highest number on the grid without lifting a pen or pencil.
Easier 9-by-9 puzzles have more numbers already filled into the grid. Harder puzzles have fewer numbers. The official Numbrix website is published by Parade magazine in an online format. The online game has hints, a timer and a solve button for daily Numbrix puzzles. Otherwise, paper copies offer puzzles to be filled in with pen or pencil.