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No change in its value (Posted on 2016-12-23) Difficulty: 4 of 5
What pandigital number's value stays unchanged when some mathematical signs are inserted between its digits.

Hint: no brackets are needed.

No Solution Yet Submitted by Ady TZIDON    
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Solution Printer's Error Numbers Comment 1 of 1
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.

  Posted by Brian Smith on 2017-07-01 13:30:46
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