71 (number)
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71 is a natural number that comes between 70 and 72. It is written as two digits in base ten, and as LXXI in Roman numerals.
71 is a prime number, meaning it has exactly two divisors: 1 and 71 itself. It is therefore not divisible by 2, 3, 5, or 7, which are the primes less than the square root of 71.
Mathematical properties
71 is the twelfth prime number, starting from 2. It forms a twin prime pair with 73, since the difference between them is two. When its digits are reversed, it gives 17, which is also prime; for this reason 71 is classified as an emirp (a prime that yields another prime when its digits are reversed).
71 is equal to the sum of three consecutive primes: 19 + 23 + 29. The sum of its proper divisors (1 only) is 1, making it a deficient number, as all prime numbers are.
General use
Like other small numbers, 71 is used as a numerical code and distinguishing mark: in years (for example, 1971 when abbreviated), highway numbers, some telephone area codes, and sports numbers. This usage has no mathematical significance; it is merely a symbol.