Numble
Numble is a 1968 board game published by Selchow and Righter which is very similar to Scrabble. Instead of forming words, players form sequences adhering to certain arithmetic and numerical constraints.[1]
Each tile in Numble has a single digit, 0 through 9, except for two blanks. A "word" in Numble is a string of digits in sequence (either ascending or descending). For example, 2,3,6,7 is a valid sequence (ascending), as is 7,6,3,2 (descending) while 3,6,7,1,1 (the same numbers) is not in sequence. Also, the sum of the digits must be a multiple of 3. (7+6+3+2=18, and 18 is 6 times 3.)
A zero is allowed at each end and duplicate digits are allowed (except for having more than one zero at either end). The following is valid; 0,2,3,6,7,0 but not 0,0,2,3,6,7 or 2,3,6,7,0,0. 1,1,3,6,7 is okay too.
Each tile is worth its digit's value in points.
A blank could be placed anywhere and, unlike in Scrabble, did not count as a particular digit, so the same blank tile could, for example, be between 3 and 4 in a horizontal sequence and between 8 and 9 in a vertical one. (This is used to get the extra points from a board square)
Some other differences from Scrabble are: a rack is six tiles instead of seven; the center square is not a "double word square"; and, playing all six tiles in your rack at once scores a 10-point bonus instead of 50.