31311721 has 4 divisors (see below), whose sum is σ = 35784832. Its totient is φ = 26838612.

The previous prime is 31311703. The next prime is 31311743. The reversal of 31311721 is 12711313.

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 31311721 - 2⁵ = 31311689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (31311701) 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, 2236545 + ... + 2236558.

It is an arithmetic number, because the mean of its divisors is an integer number (8946208).

Almost surely, 2^31311721 is an apocalyptic number.

It is an amenable number.

31311721 is a deficient number, since it is larger than the sum of its proper divisors (4473111).

31311721 is an equidigital number, since it uses as much as digits as its factorization.

31311721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4473110.

The product of its digits is 126, while the sum is 19.

The square root of 31311721 is about 5595.6877146603. The cubic root of 31311721 is about 315.1874956657.

The spelling of 31311721 in words is "thirty-one million, three hundred eleven thousand, seven hundred twenty-one".