18021881 has 4 divisors (see below), whose sum is σ = 18603264. Its totient is φ = 17440500.

The previous prime is 18021841. The next prime is 18021889. The reversal of 18021881 is 18812081.

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, and also an emirpimes, since its reverse is a distinct semiprime: 18812081 = 17 ⋅1106593.

It is a cyclic number.

It is not a de Polignac number, because 18021881 - 2¹⁴ = 18005497 is a prime.

It is a super-2 number, since 2×18021881² = 649576389556322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18021889) 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, 290645 + ... + 290706.

It is an arithmetic number, because the mean of its divisors is an integer number (4650816).

Almost surely, 2^18021881 is an apocalyptic number.

It is an amenable number.

18021881 is a deficient number, since it is larger than the sum of its proper divisors (581383).

18021881 is an equidigital number, since it uses as much as digits as its factorization.

18021881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 581382.

The product of its (nonzero) digits is 1024, while the sum is 29.

The square root of 18021881 is about 4245.2186045008. The cubic root of 18021881 is about 262.1802898319.

The spelling of 18021881 in words is "eighteen million, twenty-one thousand, eight hundred eighty-one".