75 (number)
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75 is a natural number that lies between 74 and 76. It is a composite number, meaning it has divisors other than 1 and itself. In the decimal system, it comprises two digits: 7 (tens place) and 5 (ones place).
75 is written as LXXV in Roman numerals. In binary notation it is 1001011. It is also notable that 75% is equivalent to the fraction 3/4, a ratio frequently used in percentage and quartile calculations.
Mathematical properties
The prime factorization of 75 is 3 × 5 × 5, written as 3 × 5². Its complete divisors are 1, 3, 5, 15, 25, and 75. The sum of all its divisors is 124; excluding 75 itself, the sum is 49, which is less than 75, making it a deficient number.
75 is not a perfect square, but it is squareful, as it is divisible by 25, which is a perfect square. Its square root is 5√3, approximately equal to 8.66.
Sequences in number systems
75 belongs to the sequence of nonagonal numbers, whose initial terms are 1, 9, 24, 46, 75. It is also counted among Keith numbers, which are two-digit numbers derived from a sequence whose initial digits form that number.
General usage
In chemistry, 75 is the atomic number of the element rhenium (Re). In certain cultures, a 75th anniversary is called a special 'jubilee'. The number also appears in standard measurements and administration, such as speed limits or percentage scales.