21205438255 has 4 divisors (see below), whose sum is σ = 25446525912. Its totient is φ = 16964350600.

The previous prime is 21205438229. The next prime is 21205438313. The reversal of 21205438255 is 55283450212.

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

It is not a de Polignac number, because 21205438255 - 2²⁵ = 21171883823 is a prime.

It is a super-2 number, since 2×21205438255² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2120543821 + ... + 2120543830.

It is an arithmetic number, because the mean of its divisors is an integer number (6361631478).

Almost surely, 2^21205438255 is an apocalyptic number.

21205438255 is a deficient number, since it is larger than the sum of its proper divisors (4241087657).

21205438255 is an equidigital number, since it uses as much as digits as its factorization.

21205438255 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4241087656.

The product of its (nonzero) digits is 96000, while the sum is 37.

Adding to 21205438255 its reverse (55283450212), we get a palindrome (76488888467).

The spelling of 21205438255 in words is "twenty-one billion, two hundred five million, four hundred thirty-eight thousand, two hundred fifty-five".