21715945 has 4 divisors (see below), whose sum is σ = 26059140. Its totient is φ = 17372752.

The previous prime is 21715931. The next prime is 21715951. The reversal of 21715945 is 54951712.

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 6692569 + 15023376 = 2587^2 + 3876^2 .

It is a cyclic number.

It is not a de Polignac number, because 21715945 - 2⁵ = 21715913 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21715945.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2171590 + ... + 2171599.

It is an arithmetic number, because the mean of its divisors is an integer number (6514785).

Almost surely, 2^21715945 is an apocalyptic number.

It is an amenable number.

21715945 is a deficient number, since it is larger than the sum of its proper divisors (4343195).

21715945 is an equidigital number, since it uses as much as digits as its factorization.

21715945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4343194.

The product of its digits is 12600, while the sum is 34.

The square root of 21715945 is about 4660.0370170204. The cubic root of 21715945 is about 278.9927457079.

The spelling of 21715945 in words is "twenty-one million, seven hundred fifteen thousand, nine hundred forty-five".