18221987 has 4 divisors (see below), whose sum is σ = 20825136. Its totient is φ = 15618840.

The previous prime is 18221953. The next prime is 18221989. The reversal of 18221987 is 78912281.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 78912281 = 7 ⋅11273183.

It is a cyclic number.

It is not a de Polignac number, because 18221987 - 2²⁴ = 1444771 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18221987.

It is not an unprimeable number, because it can be changed into a prime (18221989) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1301564 + ... + 1301577.

It is an arithmetic number, because the mean of its divisors is an integer number (5206284).

Almost surely, 2^18221987 is an apocalyptic number.

18221987 is a deficient number, since it is larger than the sum of its proper divisors (2603149).

18221987 is an equidigital number, since it uses as much as digits as its factorization.

18221987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2603148.

The product of its digits is 16128, while the sum is 38.

The square root of 18221987 is about 4268.7219398785. The cubic root of 18221987 is about 263.1470934746.

The spelling of 18221987 in words is "eighteen million, two hundred twenty-one thousand, nine hundred eighty-seven".