21307705 has 4 divisors (see below), whose sum is σ = 25569252. Its totient is φ = 17046160.

The previous prime is 21307687. The next prime is 21307753. The reversal of 21307705 is 50770312.

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 6230016 + 15077689 = 2496^2 + 3883^2 .

It is not a de Polignac number, because 21307705 - 2⁹ = 21307193 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21307705.

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, 2130766 + ... + 2130775.

It is an arithmetic number, because the mean of its divisors is an integer number (6392313).

Almost surely, 2^21307705 is an apocalyptic number.

It is an amenable number.

21307705 is a deficient number, since it is larger than the sum of its proper divisors (4261547).

21307705 is an equidigital number, since it uses as much as digits as its factorization.

21307705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4261546.

The product of its (nonzero) digits is 1470, while the sum is 25.

The square root of 21307705 is about 4616.0269713250. The cubic root of 21307705 is about 277.2334046505.

The spelling of 21307705 in words is "twenty-one million, three hundred seven thousand, seven hundred five".