31989721 has 4 divisors (see below), whose sum is σ = 32733712. Its totient is φ = 31245732.

The previous prime is 31989701. The next prime is 31989731. The reversal of 31989721 is 12798913.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 31989721 - 2⁷ = 31989593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (31989701) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 371931 + ... + 372016.

It is an arithmetic number, because the mean of its divisors is an integer number (8183428).

Almost surely, 2^31989721 is an apocalyptic number.

It is an amenable number.

31989721 is a deficient number, since it is larger than the sum of its proper divisors (743991).

31989721 is an equidigital number, since it uses as much as digits as its factorization.

31989721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 743990.

The product of its digits is 27216, while the sum is 40.

The square root of 31989721 is about 5655.9456326949. The cubic root of 31989721 is about 317.4462132211.

The spelling of 31989721 in words is "thirty-one million, nine hundred eighty-nine thousand, seven hundred twenty-one".