18187981 has 4 divisors (see below), whose sum is σ = 20786272. Its totient is φ = 15589692.

The previous prime is 18187973. The next prime is 18187987. The reversal of 18187981 is 18978181.

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: 18978181 = 2251 ⋅8431.

It is a cyclic number.

It is not a de Polignac number, because 18187981 - 2³ = 18187973 is a prime.

It is a super-2 number, since 2×18187981² = 661605305712722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18187987) 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, 1299135 + ... + 1299148.

It is an arithmetic number, because the mean of its divisors is an integer number (5196568).

Almost surely, 2^18187981 is an apocalyptic number.

It is an amenable number.

18187981 is a deficient number, since it is larger than the sum of its proper divisors (2598291).

18187981 is an equidigital number, since it uses as much as digits as its factorization.

18187981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2598290.

The product of its digits is 32256, while the sum is 43.

The square root of 18187981 is about 4264.7369203739. The cubic root of 18187981 is about 262.9832958881.

The spelling of 18187981 in words is "eighteen million, one hundred eighty-seven thousand, nine hundred eighty-one".