18720931 has 4 divisors (see below), whose sum is σ = 19324864. Its totient is φ = 18117000.

The previous prime is 18720907. The next prime is 18720941. The reversal of 18720931 is 13902781.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 13902781 = 709 ⋅19609.

It is a cyclic number.

It is not a de Polignac number, because 18720931 - 2⁷ = 18720803 is a prime.

It is a super-2 number, since 2×18720931² = 700946515013522, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 603901 = 18720931 / (1 + 8 + 7 + 2 + 0 + 9 + 3 + 1).

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 18720893 and 18720902.

It is not an unprimeable number, because it can be changed into a prime (18720901) 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, 301920 + ... + 301981.

It is an arithmetic number, because the mean of its divisors is an integer number (4831216).

Almost surely, 2^18720931 is an apocalyptic number.

18720931 is a deficient number, since it is larger than the sum of its proper divisors (603933).

18720931 is an equidigital number, since it uses as much as digits as its factorization.

18720931 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 603932.

The product of its (nonzero) digits is 3024, while the sum is 31.

The square root of 18720931 is about 4326.7691179447. The cubic root of 18720931 is about 265.5272805208.

The spelling of 18720931 in words is "eighteen million, seven hundred twenty thousand, nine hundred thirty-one".