21939810 has 16 divisors (see below), whose sum is σ = 52655616. Its totient is φ = 5850608.

The previous prime is 21939791. The next prime is 21939811. The reversal of 21939810 is 1893912.

It is a super-2 number, since 2×21939810² = 962710525672200, which contains 22 as substring.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (21939811) 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, 365634 + ... + 365693.

It is an arithmetic number, because the mean of its divisors is an integer number (3290976).

Almost surely, 2^21939810 is an apocalyptic number.

21939810 is an abundant number, since it is smaller than the sum of its proper divisors (30715806).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21939810 is a wasteful number, since it uses less digits than its factorization.

21939810 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 731337.

The product of its (nonzero) digits is 3888, while the sum is 33.

The square root of 21939810 is about 4683.9950896644. The cubic root of 21939810 is about 279.9481621723.

The spelling of 21939810 in words is "twenty-one million, nine hundred thirty-nine thousand, eight hundred ten".