20821863613821 has 4 divisors (see below), whose sum is σ = 27762484818432. Its totient is φ = 13881242409212.

The previous prime is 20821863613819. The next prime is 20821863613847. The reversal of 20821863613821 is 12831636812802.

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 20821863613821 - 2¹ = 20821863613819 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20821863613891) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3470310602301 + ... + 3470310602306.

It is an arithmetic number, because the mean of its divisors is an integer number (6940621204608).

Almost surely, 2^{20821863613821} is an apocalyptic number.

It is an amenable number.

20821863613821 is a deficient number, since it is larger than the sum of its proper divisors (6940621204611).

20821863613821 is an equidigital number, since it uses as much as digits as its factorization.

20821863613821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6940621204610.

The product of its (nonzero) digits is 1327104, while the sum is 51.

The spelling of 20821863613821 in words is "twenty trillion, eight hundred twenty-one billion, eight hundred sixty-three million, six hundred thirteen thousand, eight hundred twenty-one".