18221265821 has 4 divisors (see below), whose sum is σ = 19877744544. Its totient is φ = 16564787100.

The previous prime is 18221265817. The next prime is 18221265833. The reversal of 18221265821 is 12856212281.

It is a happy number.

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 18221265821 - 2² = 18221265817 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 (18221265871) 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, 828239345 + ... + 828239366.

It is an arithmetic number, because the mean of its divisors is an integer number (4969436136).

Almost surely, 2^18221265821 is an apocalyptic number.

18221265821 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

18221265821 is a deficient number, since it is larger than the sum of its proper divisors (1656478723).

18221265821 is a wasteful number, since it uses less digits than its factorization.

18221265821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1656478722.

The product of its digits is 30720, while the sum is 38.

The spelling of 18221265821 in words is "eighteen billion, two hundred twenty-one million, two hundred sixty-five thousand, eight hundred twenty-one".