A sum-product number is a number n such that the sum of n's digits times the product of n's digits is a n itself.

E.g.

135=(1+3+5) x (1 x 3 x 5)

Obviously, such a number must be divisible by it's digits as well as the sum of of it's digits.There are only three numbers such sum-product numbers, 1,135 & 144

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