21931705 has 4 divisors (see below), whose sum is σ = 26318052. Its totient is φ = 17545360.

The previous prime is 21931703. The next prime is 21931709. The reversal of 21931705 is 50713912.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3988009 + 17943696 = 1997^2 + 4236^2 .

It is not a de Polignac number, because 21931705 - 2¹ = 21931703 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21931703) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2193166 + ... + 2193175.

It is an arithmetic number, because the mean of its divisors is an integer number (6579513).

Almost surely, 2^21931705 is an apocalyptic number.

It is an amenable number.

21931705 is a deficient number, since it is larger than the sum of its proper divisors (4386347).

21931705 is an equidigital number, since it uses as much as digits as its factorization.

21931705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4386346.

The product of its (nonzero) digits is 1890, while the sum is 28.

The square root of 21931705 is about 4683.1298295051. The cubic root of 21931705 is about 279.9136851294.

The spelling of 21931705 in words is "twenty-one million, nine hundred thirty-one thousand, seven hundred five".