18905821 has 4 divisors (see below), whose sum is σ = 20624544. Its totient is φ = 17187100.

The previous prime is 18905813. The next prime is 18905851. The reversal of 18905821 is 12850981.

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 18905821 - 2³ = 18905813 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18905851) 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, 859345 + ... + 859366.

It is an arithmetic number, because the mean of its divisors is an integer number (5156136).

Almost surely, 2^18905821 is an apocalyptic number.

18905821 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

18905821 is a deficient number, since it is larger than the sum of its proper divisors (1718723).

18905821 is a wasteful number, since it uses less digits than its factorization.

18905821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1718722.

The product of its (nonzero) digits is 5760, while the sum is 34.

The square root of 18905821 is about 4348.0824509202. The cubic root of 18905821 is about 266.3985442195.

The spelling of 18905821 in words is "eighteen million, nine hundred five thousand, eight hundred twenty-one".