21786843821 has 2 divisors, whose sum is σ = 21786843822. Its totient is φ = 21786843820.

The previous prime is 21786843811. The next prime is 21786843823. The reversal of 21786843821 is 12834868712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15052836100 + 6734007721 = 122690^2 + 82061^2 .

It is a cyclic number.

It is not a de Polignac number, because 21786843821 - 2¹⁰ = 21786842797 is a prime.

It is a Sophie Germain prime.

Together with 21786843823, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21786843821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21786843823) 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 as a sum of consecutive naturals, namely, 10893421910 + 10893421911.

It is an arithmetic number, because the mean of its divisors is an integer number (10893421911).

Almost surely, 2^21786843821 is an apocalyptic number.

It is an amenable number.

21786843821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21786843821 is an equidigital number, since it uses as much as digits as its factorization.

21786843821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1032192, while the sum is 50.

The spelling of 21786843821 in words is "twenty-one billion, seven hundred eighty-six million, eight hundred forty-three thousand, eight hundred twenty-one".