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Isn't this "superfactorical" instead?
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Not exactly. The index is off by one, which actually does make the expression more complicated if you use n$ instead of n?. I hadn't seen
superfactorial before you mentioned it. Thanks for pointing it out. I think I'll try to prove that
Bell number determinant identity, equation 17 on the second linked page.
By the way, the formula f(a,b,c) is usually written quite differently (not necessarily in a way that helps here), and I think most people familiar with it would not recognize the expression I used.