Smallest value of N

7 digit........
take N =4 suppose...number of distinct number u get is 3⁴.= 81
take N =5 suppose...number of distinct number u get is 3⁵.= 243
take N =6 suppose...number of distinct number u get is 3⁶.=729
take N =7 suppose...number of distinct number u get is 3⁷.= 729*3....hence the answer

What is the answer ?

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