Number Scrabble (also known as Pick15^[1][2][3] or 3 to 15^[4]) is a mathematical game where players take turns to select numbers from 1 to 9 without repeating any numbers previously used, and the first player with a sum of exactly 15 using any three of their number selections wins the game.^[5][6] The game is isomorphic to tic-tac-toe, as can be seen if the game is mapped onto a magic square.^[6]

Number Scrabble is played with the list of numbers between 1 and 9. Each player takes turns picking a number from the list. Once a number has been picked, it cannot be picked again. If a player has picked three numbers that add up to 15, that player wins the game.^[5][6][7] However, if all the numbers are used and no player gets exactly 15, the game is a draw.^[5][6]

The game is identical to tic-tac-toe, as can be seen by reference to a 3x3 magic square: if a player has selected three numbers which can be found in a line on a magic square, they will add up to 15. If they have selected any other three numbers, they will not.^[8]

As an example game between player A and player B:

1. A picks 9.
2. B picks 8.
3. A picks 2.
4. B has no choice but to pick 4 (otherwise, A could get 9+2+4=15).
5. A has no choice but to pick 3 (otherwise, B could get 8+4+3=15).
6. B picks 6, and thereby threatens to win by either picking 1 (8+6+1=15) or 5 (4+6+5=15).
7. At this point, A has lost because the second pick (2) was a mistake, A should not pick 1, 2, 3, or 7 as second pick, or A must lose.

v t e Tic-tac-toe
Variants	3D tic-tac-toe Gomoku Notakto Treblecross Number Scrabble Order and Chaos Pente Quantum tic-tac-toe Renju SOS Ultimate tic-tac-toe Wild tic-tac-toe
Related concepts	m,n,k-game nd game Kaplansky's game Harary's generalized tic-tac-toe Hales–Jewett theorem Strategy-stealing argument Futile game Paper-and-pencil game
Similar games	Nine men's morris Score Four Tic-Stac-Toe Gobblet Quarto Three men's morris Nine Holes Achi Connect Four Connect6 OXO Toss Across Pentago

v t e Magic polygons
Types	Magic circle Magic hexagon Magic hexagram Magic square Magic star Magic triangle
Related shapes	Alphamagic square Antimagic square Geomagic square Heterosquare Pandiagonal magic square Prime reciprocal magic square Most-perfect magic square
Higher dimensional shapes	Magic cube classes Magic hypercube Magic hyperbeam
Classification	Associative magic square Pandiagonal magic square Multimagic square
Related concepts	Latin square Word square Number Scrabble Eight queens puzzle Magic constant Magic graph Magic series