If we're talking mathematicians, you just know it's going to be ω-nested recursive functions any moment now. Just be grateful it's not all n with polynomial subscripts or something.
Uhh, I'm pretty sure I've seen that, but I'm not sure where now. Any time you need to access a member of a list or array that's determined by a polynomial - which by Horner's rule covers all combinations of multiplications and additions - it would be a possible notation.