21948809 has 2 divisors, whose sum is σ = 21948810. Its totient is φ = 21948808.

The previous prime is 21948799. The next prime is 21948811. The reversal of 21948809 is 90884912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11580409 + 10368400 = 3403^2 + 3220^2 .

It is a cyclic number.

It is not a de Polignac number, because 21948809 - 2⁴ = 21948793 is a prime.

Together with 21948811, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21945809) 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, 10974404 + 10974405.

It is an arithmetic number, because the mean of its divisors is an integer number (10974405).

Almost surely, 2^21948809 is an apocalyptic number.

It is an amenable number.

21948809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21948809 is an equidigital number, since it uses as much as digits as its factorization.

21948809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 41472, while the sum is 41.

The square root of 21948809 is about 4684.9556027779. The cubic root of 21948809 is about 279.9864321657.

The spelling of 21948809 in words is "twenty-one million, nine hundred forty-eight thousand, eight hundred nine".