I have found a 3-digit perfect square, a 3-digit perfect cube and a 4-digit triangular number that between them use 10 different digits, with no leading zero. (Triangular numbers are those that fit ...

From Oscar Lanzi comes a matter of tricky triangular numbers: Suppose you are adding up whole numbers in order. You start with 1, then add 2 to get 3. Then you add 3 to get 6. Then you add 4 to get 10 ...