What pandigital number's value stays unchanged when some mathematical signs are inserted between its digits.
Hint: no brackets are needed.
Restricting the operators to multiplication and exponentiation seems to be a sensible starting point. Then I can find 2592 = 2^5*9^2 and 35721 = 3^5*7*21 fairly easily.
This is enough to find
A156322 in the OEIS. In their notes: "
3^5*1482*9760=3514829760 is the only pandigital with this property."
Subsequences of this sequence include
A096298 and
A116890. These are the Printer's Error sequences; sequences where the inserted operators alternate between multiplication and exponentiation.
Also,
A157198 is a generalization where all five basic operators are used.
Printer's Error Numbers