18977821 has 4 divisors (see below), whose sum is σ = 18992700. Its totient is φ = 18962944.

The previous prime is 18977813. The next prime is 18977843. The reversal of 18977821 is 12877981.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 4644025 + 14333796 = 2155^2 + 3786^2 .

It is a cyclic number.

It is not a de Polignac number, because 18977821 - 2³ = 18977813 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 (18977891) 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, 5326 + ... + 8143.

It is an arithmetic number, because the mean of its divisors is an integer number (4748175).

Almost surely, 2^18977821 is an apocalyptic number.

It is an amenable number.

18977821 is a deficient number, since it is larger than the sum of its proper divisors (14879).

18977821 is a wasteful number, since it uses less digits than its factorization.

18977821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14878.

The product of its digits is 56448, while the sum is 43.

The square root of 18977821 is about 4356.3540948826. The cubic root of 18977821 is about 266.7362955330.

The spelling of 18977821 in words is "eighteen million, nine hundred seventy-seven thousand, eight hundred twenty-one".