20813210857 has 4 divisors (see below), whose sum is σ = 22037517396. Its totient is φ = 19588904320.

The previous prime is 20813210833. The next prime is 20813210861. The reversal of 20813210857 is 75801231802.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9092766736 + 11720444121 = 95356^2 + 108261^2 .

It is a cyclic number.

It is not a de Polignac number, because 20813210857 - 2⁷ = 20813210729 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20813210057) 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, 612153244 + ... + 612153277.

It is an arithmetic number, because the mean of its divisors is an integer number (5509379349).

Almost surely, 2^20813210857 is an apocalyptic number.

It is an amenable number.

20813210857 is a deficient number, since it is larger than the sum of its proper divisors (1224306539).

20813210857 is a wasteful number, since it uses less digits than its factorization.

20813210857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1224306538.

The product of its (nonzero) digits is 26880, while the sum is 37.

The spelling of 20813210857 in words is "twenty billion, eight hundred thirteen million, two hundred ten thousand, eight hundred fifty-seven".