65 (number)
From Halbeeg, the open encyclopedia · Af-Soomaali
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65 is a natural number that falls between 64 and 66. In the decimal system, it consists of two digits: 6 in the tens place and 5 in the ones place. In Roman numerals, it is written as LXV.
65 is a composite number, meaning it has factors other than 1 and itself. Its factors are 1, 5, 13, and 65. It can therefore be expressed as the product of two prime numbers: 5 × 13.
Mathematical properties
65 is the sum of two perfect squares in two different ways: 1² + 8² = 1 + 64 = 65, and 4² + 7² = 16 + 49 = 65. This property makes it a notable example in the study of numbers expressible as the sum of two squares.
65 is also classified as an octagonal number and a cake number in mathematical sequences. Another property is that the sum of its digits (6 + 5 = 11) is a composite number, and it ends in 5, which confirms its divisibility by 5.
Common usage
Many countries established 65 years as the standard retirement age from formal employment, though this has been changed in many places in recent years. Some education systems and health services use 65 as a threshold to divide age groups. In demographic data, the group aged 65 and over is a frequently used indicator for measuring the aging of a population.
In other number systems, 65 corresponds to 1000001 in binary and 41 in hexadecimal. In ASCII code standards, the value 65 is assigned to the uppercase letter 'A'.