I'm 21 now!

[cheesehead]

Originally Posted by xilman

And which of those square roots are themselves triangular?

Originally Posted by wblipp

Yes, cheesehead seems to have forgotten that the square root must also be a triangular number.

I didn't forget, but I did misunderstand MathWorld's reference to A001110, and I misread 36 in A001109 as "35", which gave pretty much the same effect.

MathWorld's your friend, but sometimes you need better glasses to appreciate a friend. I'm putting that on my to-do list.