18321981 has 4 divisors (see below), whose sum is σ = 24429312. Its totient is φ = 12214652.

The previous prime is 18321977. The next prime is 18321991. The reversal of 18321981 is 18912381.

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.

It is a cyclic number.

It is not a de Polignac number, because 18321981 - 2² = 18321977 is a prime.

It is a super-2 number, since 2×18321981² = 671389975528722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18321991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3053661 + ... + 3053666.

It is an arithmetic number, because the mean of its divisors is an integer number (6107328).

Almost surely, 2^18321981 is an apocalyptic number.

It is an amenable number.

18321981 is a deficient number, since it is larger than the sum of its proper divisors (6107331).

18321981 is an equidigital number, since it uses as much as digits as its factorization.

18321981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6107330.

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

The square root of 18321981 is about 4280.4183206785. The cubic root of 18321981 is about 263.6275596491.

The spelling of 18321981 in words is "eighteen million, three hundred twenty-one thousand, nine hundred eighty-one".