The two numbers that meet the criteria of having every digit except 0 appearing just once in the number and in its square are 1 and 76.
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1:
- The square of 1 is \(1^2 = 1\). The only digit is 1, which meets the requirement.
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76:
- The square of 76 is \(76^2 = 5776\). The digits in 76 are 7 and 6, appearing once each. In 5776, the digits 5, 7, and 6 also satisfy the condition (0 is excluded).
No other two-digit or three-digit numbers seem to fit this property based on the constraints you provided.