21364391821 has 4 divisors (see below), whose sum is σ = 21364699644. Its totient is φ = 21364084000.

The previous prime is 21364391801. The next prime is 21364391837. The reversal of 21364391821 is 12819346312.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 12261132900 + 9103258921 = 110730^2 + 95411^2 .

It is a cyclic number.

It is not a de Polignac number, because 21364391821 - 2²⁵ = 21330837389 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 (21364391801) 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, 4641 + ... + 206761.

It is an arithmetic number, because the mean of its divisors is an integer number (5341174911).

Almost surely, 2^21364391821 is an apocalyptic number.

It is an amenable number.

21364391821 is a deficient number, since it is larger than the sum of its proper divisors (307823).

21364391821 is a wasteful number, since it uses less digits than its factorization.

21364391821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 307822.

The product of its digits is 62208, while the sum is 40.

The spelling of 21364391821 in words is "twenty-one billion, three hundred sixty-four million, three hundred ninety-one thousand, eight hundred twenty-one".