By Thanos Stantzouris
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A sum-product number is an integer that in a given base is equal to the sum of its digits times the product of its digits. Or, to put it algebraically, given an integer n that is l digits long in base b (with dx representing the xth digit), if

n = (\sum_{i = 1}^l d_i)(\prod_{j = 1}^l d_j)

then n is a sum-product number in base b. In base 10, the only sum-product numbers are 0, 1, 135, 144 (sequence A038369 in the OEIS).
Thus, for example, 144 is a sum-product number because 1 + 4 + 4 = 9, and 1 × 4 × 4 = 16, and 9 × 16 = 144.

Write a program in a C language that will find it and display all the numbers that meet the above property and are less than 1000. In the end, their crowd should also be displayed.