2564636821 has 2 divisors, whose sum is σ = 2564636822. Its totient is φ = 2564636820.

The previous prime is 2564636819. The next prime is 2564636923. The reversal of 2564636821 is 1286364652.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 2548836196 + 15800625 = 50486^2 + 3975^2 .

It is a cyclic number.

It is not a de Polignac number, because 2564636821 - 2¹ = 2564636819 is a prime.

Together with 2564636819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2564636021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1282318410 + 1282318411.

It is an arithmetic number, because the mean of its divisors is an integer number (1282318411).

Almost surely, 2^2564636821 is an apocalyptic number.

It is an amenable number.

2564636821 is a deficient number, since it is larger than the sum of its proper divisors (1).

2564636821 is an equidigital number, since it uses as much as digits as its factorization.

2564636821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 414720, while the sum is 43.

The square root of 2564636821 is about 50642.2434435916. The cubic root of 2564636821 is about 1368.8061813126.

The spelling of 2564636821 in words is "two billion, five hundred sixty-four million, six hundred thirty-six thousand, eight hundred twenty-one".