18978921 has 32 divisors (see below), whose sum is σ = 30576000. Its totient is φ = 11565504.

The previous prime is 18978917. The next prime is 18978959. The reversal of 18978921 is 12987981.

It is not a de Polignac number, because 18978921 - 2² = 18978917 is a prime.

It is not an unprimeable number, because it can be changed into a prime (18978901) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 48595 + ... + 48983.

It is an arithmetic number, because the mean of its divisors is an integer number (955500).

Almost surely, 2^18978921 is an apocalyptic number.

It is an amenable number.

18978921 is a deficient number, since it is larger than the sum of its proper divisors (11597079).

18978921 is a wasteful number, since it uses less digits than its factorization.

18978921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 550 (or 544 counting only the distinct ones).

The product of its digits is 72576, while the sum is 45.

The square root of 18978921 is about 4356.4803454165. The cubic root of 18978921 is about 266.7414489918.

The spelling of 18978921 in words is "eighteen million, nine hundred seventy-eight thousand, nine hundred twenty-one".