Fiftyis the smallest number that is the sum of two non-zero square numbers in two distinct ways: 50 = 1^{2}+ 7^{2}= 5^{2}+ 5^{2}.^{[1]}It is also the sum of three squares, 50 = 3^{2}+ 4^{2}+ 5^{2}. 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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