Seems unique

I am thinking of a positive integer.

  • It is three larger than a prime number.

  • Sum of its digits equal to 11.

  • Sum of its divisors is equal to 120.

What is the positive integer?


The answer is 56.

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1 solution

Chris Lewis
Oct 29, 2019

Say the mystery number is n n .

Since n n is 3 3 more than a prime (and that prime is clearly not 2 2 ), n n must be even.

Since n n is a divisor of itself, and the sum of its divisors is 120 120 , we must have n < 120 n<120 .

There are only four even numbers less than 120 120 with digit sum 11 11 : 38 , 56 , 74 , 92 38,56,74,92

It's easy to check that, of these, only 56 \boxed{56} has the correct divisor sum.

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