18213981 has 8 divisors (see below), whose sum is σ = 24536064. Its totient is φ = 12017280.

The previous prime is 18213977. The next prime is 18214039. The reversal of 18213981 is 18931281.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 18213981 - 2² = 18213977 is a prime.

It is a super-2 number, since 2×18213981² = 663498207736722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18213911) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 31005 + ... + 31586.

It is an arithmetic number, because the mean of its divisors is an integer number (3067008).

Almost surely, 2^18213981 is an apocalyptic number.

It is an amenable number.

18213981 is a deficient number, since it is larger than the sum of its proper divisors (6322083).

18213981 is an equidigital number, since it uses as much as digits as its factorization.

18213981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62691.

The product of its digits is 3456, while the sum is 33.

The square root of 18213981 is about 4267.7840854476. The cubic root of 18213981 is about 263.1085491188.

The spelling of 18213981 in words is "eighteen million, two hundred thirteen thousand, nine hundred eighty-one".