21564877819 has 4 divisors (see below), whose sum is σ = 21603181896. Its totient is φ = 21526573744.

The previous prime is 21564877813. The next prime is 21564877837. The reversal of 21564877819 is 91877846512.

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 21564877819 - 2⁵ = 21564877787 is a prime.

It is a super-2 number, since 2×21564877819² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21564877813) 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, 19151194 + ... + 19152319.

It is an arithmetic number, because the mean of its divisors is an integer number (5400795474).

Almost surely, 2^21564877819 is an apocalyptic number.

21564877819 is a deficient number, since it is larger than the sum of its proper divisors (38304077).

21564877819 is an equidigital number, since it uses as much as digits as its factorization.

21564877819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38304076.

The product of its digits is 6773760, while the sum is 58.

The spelling of 21564877819 in words is "twenty-one billion, five hundred sixty-four million, eight hundred seventy-seven thousand, eight hundred nineteen".