Wow that was hard! More like Mystery Hunt than a crossword puzzle. (My completion time is a total fiction… I was noodling in my head, on paper, in Excel, and Googling, probably for a couple hours in total, all “off the clock”!) I had to use several checks and reveal six squares before I could “finish”.
Loved a lot of the clues, and 23A in particular was a brilliant misdirect. A few entries I still don’t get (any explanations appreciated):
13A — what does it mean? I don’t see how 7722 is the product of any consecutive integers.
14A — when I cube 5424 I get 159572865024, which has no 3 digit. (I think 5224^3 = 142563879424 which is a “pandigit”.)
29D — I was sure this would end up being the same as the factorial of the digit sum, but (obviously) it’s something else… just can’t figure out what.
37A — no idea.
40A — I see how 296791683235499000 ends with “ddd” but I don’t get how it starts with “ddd”.