31523721 has 4 divisors (see below), whose sum is σ = 42031632. Its totient is φ = 21015812.

The previous prime is 31523707. The next prime is 31523749. The reversal of 31523721 is 12732513.

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 31523721 - 2⁹ = 31523209 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 31523691 and 31523700.

It is not an unprimeable number, because it can be changed into a prime (31523761) 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, 5253951 + ... + 5253956.

It is an arithmetic number, because the mean of its divisors is an integer number (10507908).

Almost surely, 2^31523721 is an apocalyptic number.

It is an amenable number.

31523721 is a deficient number, since it is larger than the sum of its proper divisors (10507911).

31523721 is a wasteful number, since it uses less digits than its factorization.

31523721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10507910.

The product of its digits is 1260, while the sum is 24.

The square root of 31523721 is about 5614.5989171089. The cubic root of 31523721 is about 315.8972353177.

The spelling of 31523721 in words is "thirty-one million, five hundred twenty-three thousand, seven hundred twenty-one".