Sigma of P(n)

     Let's define a function over the non-negative integers in the following manner:

  1. P(n) = n when n is a one-digit integer.

  2. P(n) = the product of all the digits of n when n > 9.

     Example: P(1729) = 126, because 1 × 7 × 2 × 9 = 126.

     Evaluate the following:

Note: this problem was shared to WTM by Reza Kassai, of Shiraz, Iran.

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