18221491 has 4 divisors (see below), whose sum is σ = 18234112. Its totient is φ = 18208872.

The previous prime is 18221479. The next prime is 18221509. The reversal of 18221491 is 19412281.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18221491 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18221431) 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, 3816 + ... + 7141.

It is an arithmetic number, because the mean of its divisors is an integer number (4558528).

Almost surely, 2^18221491 is an apocalyptic number.

18221491 is a deficient number, since it is larger than the sum of its proper divisors (12621).

18221491 is a wasteful number, since it uses less digits than its factorization.

18221491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12620.

The product of its digits is 1152, while the sum is 28.

The square root of 18221491 is about 4268.6638424687. The cubic root of 18221491 is about 263.1447058436.

The spelling of 18221491 in words is "eighteen million, two hundred twenty-one thousand, four hundred ninety-one".