18101981 has 4 divisors (see below), whose sum is σ = 18331200. Its totient is φ = 17872764.

The previous prime is 18101971. The next prime is 18102013. The reversal of 18101981 is 18910181.

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 18101981 - 2¹⁴ = 18085597 is a prime.

It is a super-2 number, since 2×18101981² = 655363432248722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18101971) 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, 114491 + ... + 114648.

It is an arithmetic number, because the mean of its divisors is an integer number (4582800).

Almost surely, 2^18101981 is an apocalyptic number.

It is an amenable number.

18101981 is a deficient number, since it is larger than the sum of its proper divisors (229219).

18101981 is an equidigital number, since it uses as much as digits as its factorization.

18101981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 229218.

The product of its (nonzero) digits is 576, while the sum is 29.

The square root of 18101981 is about 4254.6422881366. The cubic root of 18101981 is about 262.5681443643.

The spelling of 18101981 in words is "eighteen million, one hundred one thousand, nine hundred eighty-one".