The number with no new digits

There is a 66-digit integer NN such that each of 2N,3N,4N,5N,6N2N, 3N, 4N, 5N, 6N uses exactly the same set of digits as NN (indeed each product is a rearrangement of NN's digits). What is NN?

Show hints (2)+
  1. Think about the decimal expansion of a simple fraction whose digits cycle.
  2. It's the repeating block of 1/71/7: 142857142857. Its multiples 2×,,6×2\times,\dots,6\times are rotations of it.

Answer

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142857

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Asked at: Jane Street, Citadel

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