21873809 has 2 divisors, whose sum is σ = 21873810. Its totient is φ = 21873808.

The previous prime is 21873779. The next prime is 21873821. The reversal of 21873809 is 90837812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21827584 + 46225 = 4672^2 + 215^2 .

It is a cyclic number.

It is not a de Polignac number, because 21873809 - 2¹² = 21869713 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21873829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10936904 + 10936905.

It is an arithmetic number, because the mean of its divisors is an integer number (10936905).

Almost surely, 2^21873809 is an apocalyptic number.

It is an amenable number.

21873809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21873809 is an equidigital number, since it uses as much as digits as its factorization.

21873809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 24192, while the sum is 38.

The square root of 21873809 is about 4676.9444084787. The cubic root of 21873809 is about 279.6671597767.

The spelling of 21873809 in words is "twenty-one million, eight hundred seventy-three thousand, eight hundred nine".