I often whip these up on a piece of scrap paper on my desk while students are working and I can see they will need an extension activity. Simply think of times table sums (eg. 3x2=6, 2x5=10, 2x4=8...) and then put each number into its own box in a table.
Children write the boggle into their maths book, and then write any sums they see. They may need to start again if they get to the end and have numbers left over that don't fit!
Pretty quickly they realise that they need to work backwards, and start with the biggest numbers, and check the factors that may add to that number. Some BRILLIANT maths problem solving!