71809 has 2 divisors, whose sum is σ = 71810. Its totient is φ = 71808.

The previous prime is 71807. The next prime is 71821. The reversal of 71809 is 90817.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 48400 + 23409 = 220^2 + 153^2 .

It is a cyclic number.

It is not a de Polignac number, because 71809 - 2¹ = 71807 is a prime.

Together with 71807, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (71807) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 35904 + 35905.

It is an arithmetic number, because the mean of its divisors is an integer number (35905).

2⁷¹⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

71809 is a deficient number, since it is larger than the sum of its proper divisors (1).

71809 is an equidigital number, since it uses as much as digits as its factorization.

71809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 504, while the sum is 25.

The square root of 71809 is about 267.9720134641. The cubic root of 71809 is about 41.5648572165.

It can be divided in two parts, 7180 and 9, that multiplied together give a triangular number (64620 = T₃₅₉).

The spelling of 71809 in words is "seventy-one thousand, eight hundred nine".