Fifty

Fifty is the smallest number that is the sum of two non-zero square numbers in two distinct ways: 50 = 1² + 7² = 5² + 5².^[1] It is also the sum of three squares, 50 = 3² + 4² + 5². It is a Harshad number.

There is no solution to the equation φ(x) = 50, making 50 a nontotient. Nor is there a solution to the equation x – φ(x) = 50, making 50 a noncototient.

The aliquot sum of 50 is 43 and its aliquot sequence is (50,43,1,0). Fifty is itself the aliquot sum of 40 and 94.

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