21901809 has 8 divisors (see below), whose sum is σ = 29226400. Its totient is φ = 14589216.

The previous prime is 21901799. The next prime is 21901811. The reversal of 21901809 is 90810912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21901809 - 2⁴ = 21901793 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21901829) 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 in 7 ways as a sum of consecutive naturals, for example, 2949 + ... + 7245.

It is an arithmetic number, because the mean of its divisors is an integer number (3653300).

Almost surely, 2^21901809 is an apocalyptic number.

It is an amenable number.

21901809 is a deficient number, since it is larger than the sum of its proper divisors (7324591).

21901809 is a wasteful number, since it uses less digits than its factorization.

21901809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5999.

The product of its (nonzero) digits is 1296, while the sum is 30.

The square root of 21901809 is about 4679.9368585484. The cubic root of 21901809 is about 279.7864400474.

The spelling of 21901809 in words is "twenty-one million, nine hundred one thousand, eight hundred nine".