21640872821 has 4 divisors (see below), whose sum is σ = 21914808000. Its totient is φ = 21366937644.

The previous prime is 21640872817. The next prime is 21640872829. The reversal of 21640872821 is 12827804612.

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 a cyclic number.

It is not a de Polignac number, because 21640872821 - 2² = 21640872817 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 (21640872829) 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, 136967471 + ... + 136967628.

It is an arithmetic number, because the mean of its divisors is an integer number (5478702000).

Almost surely, 2^21640872821 is an apocalyptic number.

It is an amenable number.

21640872821 is a deficient number, since it is larger than the sum of its proper divisors (273935179).

21640872821 is an equidigital number, since it uses as much as digits as its factorization.

21640872821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 273935178.

The product of its (nonzero) digits is 86016, while the sum is 41.

The spelling of 21640872821 in words is "twenty-one billion, six hundred forty million, eight hundred seventy-two thousand, eight hundred twenty-one".