31491721 has 4 divisors (see below), whose sum is σ = 33149200. Its totient is φ = 29834244.

The previous prime is 31491697. The next prime is 31491727. The reversal of 31491721 is 12719413.

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 31491721 - 2¹¹ = 31489673 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 31491721.

It is not an unprimeable number, because it can be changed into a prime (31491727) 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, 828711 + ... + 828748.

It is an arithmetic number, because the mean of its divisors is an integer number (8287300).

Almost surely, 2^31491721 is an apocalyptic number.

It is an amenable number.

31491721 is a deficient number, since it is larger than the sum of its proper divisors (1657479).

31491721 is a wasteful number, since it uses less digits than its factorization.

31491721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1657478.

The product of its digits is 1512, while the sum is 28.

The square root of 31491721 is about 5611.7484797521. The cubic root of 31491721 is about 315.7903091299.

The spelling of 31491721 in words is "thirty-one million, four hundred ninety-one thousand, seven hundred twenty-one".