21939809 has 8 divisors (see below), whose sum is σ = 23612328. Its totient is φ = 20309760.

The previous prime is 21939791. The next prime is 21939811. The reversal of 21939809 is 90893912.

It can be written as a sum of positive squares in 4 ways, for example, as 112225 + 21827584 = 335^2 + 4672^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21939809 - 2¹² = 21935713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21939829) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9542 + ... + 11615.

It is an arithmetic number, because the mean of its divisors is an integer number (2951541).

Almost surely, 2^21939809 is an apocalyptic number.

It is an amenable number.

21939809 is a deficient number, since it is larger than the sum of its proper divisors (1672519).

21939809 is a wasteful number, since it uses less digits than its factorization.

21939809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21235.

The product of its (nonzero) digits is 34992, while the sum is 41.

The square root of 21939809 is about 4683.9949829179. The cubic root of 21939809 is about 279.9481579190.

The spelling of 21939809 in words is "twenty-one million, nine hundred thirty-nine thousand, eight hundred nine".