Yes. It's a square number.
It is a tough puzzle, but it's a rewarding one. Someone likened it to climbing a rock face, looking for one hand- or foothold at a time, which is a good description. It's just that finding each hold requires ingenuity and flexible thinking. And like climbing a mountain, there's a sense of euphoria when you get to the top.
Normally I do the workings for the number puzzles on the actual page in The Times, but I had to be a bit more organised for this one. If you use a spreadsheet, do the lower case letters in italics. I didn't, so I misread lowercase L (l) for uppercase i (I) and had to start again.