71809821 has 10 divisors (see below), whose sum is σ = 107271582. Its totient is φ = 47873160.

The previous prime is 71809799. The next prime is 71809847. The reversal of 71809821 is 12890817.

It can be written as a sum of positive squares in only one way, i.e., 38007225 + 33802596 = 6165^2 + 5814^2 .

It is not a de Polignac number, because 71809821 - 2¹⁰ = 71808797 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (71809021) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 443190 + ... + 443351.

Almost surely, 2^71809821 is an apocalyptic number.

It is an amenable number.

71809821 is a deficient number, since it is larger than the sum of its proper divisors (35461761).

71809821 is an equidigital number, since it uses as much as digits as its factorization.

71809821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 886553 (or 886544 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 71809821 is about 8474.0675593247. The cubic root of 71809821 is about 415.6501562100.

The spelling of 71809821 in words is "seventy-one million, eight hundred nine thousand, eight hundred twenty-one".