21972809 has 2 divisors, whose sum is σ = 21972810. Its totient is φ = 21972808.

The previous prime is 21972803. The next prime is 21972833. The reversal of 21972809 is 90827912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19998784 + 1974025 = 4472^2 + 1405^2 .

It is a cyclic number.

It is not a de Polignac number, because 21972809 - 2⁸ = 21972553 is a prime.

It is not a weakly prime, because it can be changed into another prime (21972803) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10986404 + 10986405.

It is an arithmetic number, because the mean of its divisors is an integer number (10986405).

Almost surely, 2^21972809 is an apocalyptic number.

It is an amenable number.

21972809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21972809 is an equidigital number, since it uses as much as digits as its factorization.

21972809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 21972809 is about 4687.5162933050. The cubic root of 21972809 is about 280.0884456985.

The spelling of 21972809 in words is "twenty-one million, nine hundred seventy-two thousand, eight hundred nine".