Triangular number that are also square . There exist triangular numbers that are also square Wonder of wonders. I couldn't help dropping this note to point out the curious fact that there is also an infinite set of numbers which are simultaneously both triangular and square.
Proof is fairly straightforward.
Yes, of course. 2 Armando Guarnaschelli from Argentina found a very simple recurrence relation that generates all triangular numbers that are also square. Alexander Bogomolny 2789738 .