1 to 9 is the name of a twitter account linked to https://maththinkblog.wordpress.com/. It uses several puzzle formats, one of them is this:
fill in the digits 1 to 9 all exactly once in this square. The digit 4 has already been given. The numbers along side the square are the sum of the numbers in the diagonal, row or column.
You can check your solutions here
New puzzles are published at least twice a month on Fridays. Solutions are published after one or more weeks. You are welcome to remark on the difficulty level of the puzzles, discuss alternate solutions, and so on. Puzzles are rated on a scale of 1 to 5 stars.
justpuzzles 