31240861721 has 4 divisors (see below), whose sum is σ = 31251429732. Its totient is φ = 31230293712.

The previous prime is 31240861703. The next prime is 31240861747. The reversal of 31240861721 is 12716804213.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12716804213 = 23 ⋅552904531.

It can be written as a sum of positive squares in 2 ways, for example, as 4733440000 + 26507421721 = 68800^2 + 162811^2 .

It is a cyclic number.

It is not a de Polignac number, because 31240861721 - 2¹⁰ = 31240860697 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (31240861781) 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, 5279570 + ... + 5285483.

It is an arithmetic number, because the mean of its divisors is an integer number (7812857433).

Almost surely, 2^31240861721 is an apocalyptic number.

It is an amenable number.

31240861721 is a deficient number, since it is larger than the sum of its proper divisors (10568011).

31240861721 is a wasteful number, since it uses less digits than its factorization.

31240861721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10568010.

The product of its (nonzero) digits is 16128, while the sum is 35.

The spelling of 31240861721 in words is "thirty-one billion, two hundred forty million, eight hundred sixty-one thousand, seven hundred twenty-one".