21542905821 has 4 divisors (see below), whose sum is σ = 28723874432. Its totient is φ = 14361937212.

The previous prime is 21542905781. The next prime is 21542905829. The reversal of 21542905821 is 12850924512.

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 not a de Polignac number, because 21542905821 - 2¹¹ = 21542903773 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21542905821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21542905829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3590484301 + ... + 3590484306.

It is an arithmetic number, because the mean of its divisors is an integer number (7180968608).

Almost surely, 2^21542905821 is an apocalyptic number.

It is an amenable number.

21542905821 is a deficient number, since it is larger than the sum of its proper divisors (7180968611).

21542905821 is an equidigital number, since it uses as much as digits as its factorization.

21542905821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7180968610.

The product of its (nonzero) digits is 57600, while the sum is 39.

The spelling of 21542905821 in words is "twenty-one billion, five hundred forty-two million, nine hundred five thousand, eight hundred twenty-one".