21821768657 has 4 divisors (see below), whose sum is σ = 23500366260. Its totient is φ = 20143171056.

The previous prime is 21821768653. The next prime is 21821768659. The reversal of 21821768657 is 75686712812.

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 14835483601 + 6986285056 = 121801^2 + 83584^2 .

It is a cyclic number.

It is not a de Polignac number, because 21821768657 - 2² = 21821768653 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21821768599 and 21821768608.

It is not an unprimeable number, because it can be changed into a prime (21821768653) 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, 839298782 + ... + 839298807.

It is an arithmetic number, because the mean of its divisors is an integer number (5875091565).

Almost surely, 2^21821768657 is an apocalyptic number.

It is an amenable number.

21821768657 is a deficient number, since it is larger than the sum of its proper divisors (1678597603).

21821768657 is a wasteful number, since it uses less digits than its factorization.

21821768657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1678597602.

The product of its digits is 2257920, while the sum is 53.

The spelling of 21821768657 in words is "twenty-one billion, eight hundred twenty-one million, seven hundred sixty-eight thousand, six hundred fifty-seven".