18021931 has 4 divisors (see below), whose sum is σ = 18034432. Its totient is φ = 18009432.

The previous prime is 18021907. The next prime is 18021947. The reversal of 18021931 is 13912081.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 13912081 = 67 ⋅207643.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18021931 is a prime.

It is a super-2 number, since 2×18021931² = 649579993937522, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 18021896 and 18021905.

It is not an unprimeable number, because it can be changed into a prime (18021131) 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, 3756 + ... + 7081.

It is an arithmetic number, because the mean of its divisors is an integer number (4508608).

Almost surely, 2^18021931 is an apocalyptic number.

18021931 is a deficient number, since it is larger than the sum of its proper divisors (12501).

18021931 is a wasteful number, since it uses less digits than its factorization.

18021931 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12500.

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 18021931 is about 4245.2244934750. The cubic root of 18021931 is about 262.1805322965.

The spelling of 18021931 in words is "eighteen million, twenty-one thousand, nine hundred thirty-one".