21205557215 has 4 divisors (see below), whose sum is σ = 25446668664. Its totient is φ = 16964445768.

The previous prime is 21205557187. The next prime is 21205557239. The reversal of 21205557215 is 51275550212.

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

It is a cyclic number.

It is not a de Polignac number, because 21205557215 - 2⁸ = 21205556959 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2120555717 + ... + 2120555726.

It is an arithmetic number, because the mean of its divisors is an integer number (6361667166).

Almost surely, 2^21205557215 is an apocalyptic number.

21205557215 is a deficient number, since it is larger than the sum of its proper divisors (4241111449).

21205557215 is an equidigital number, since it uses as much as digits as its factorization.

21205557215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4241111448.

The product of its (nonzero) digits is 35000, while the sum is 35.

The spelling of 21205557215 in words is "twenty-one billion, two hundred five million, five hundred fifty-seven thousand, two hundred fifteen".