21939905 has 8 divisors (see below), whose sum is σ = 28353192. Its totient is φ = 16201728.

The previous prime is 21939881. The next prime is 21939919. The reversal of 21939905 is 50993912.

It can be written as a sum of positive squares in 4 ways, for example, as 49 + 21939856 = 7^2 + 4684^2 .

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 21939905 - 2⁸ = 21939649 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 168704 + ... + 168833.

It is an arithmetic number, because the mean of its divisors is an integer number (3544149).

Almost surely, 2^21939905 is an apocalyptic number.

It is an amenable number.

21939905 is a deficient number, since it is larger than the sum of its proper divisors (6413287).

21939905 is a wasteful number, since it uses less digits than its factorization.

21939905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 337555.

The product of its (nonzero) digits is 21870, while the sum is 38.

The square root of 21939905 is about 4684.0052305692. The cubic root of 21939905 is about 279.9485662329.

The spelling of 21939905 in words is "twenty-one million, nine hundred thirty-nine thousand, nine hundred five".