In the grid shown on the left place eight digits from 1 through 8 - one digit per circle - in such a way that numbers that differ only by 1 (1 and 2, 2 and 3, 3 an 4, etc.) will not be placed in circles directly connected by a straight line.

http://www.puzzles.com/PuzzlePlayground/NumberGrid/NumberGrid.htm

Here is a paper-and-pencil version of the puzzle.

http://www.puzzles.com/PuzzlePlayground/NumberGrid/NumberGridPuzzlePrint...