21520705 has 4 divisors (see below), whose sum is σ = 25824852. Its totient is φ = 17216560.

The previous prime is 21520699. The next prime is 21520721. The reversal of 21520705 is 50702512.

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 2961841 + 18558864 = 1721^2 + 4308^2 .

It is not a de Polignac number, because 21520705 - 2⁹ = 21520193 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

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, 2152066 + ... + 2152075.

It is an arithmetic number, because the mean of its divisors is an integer number (6456213).

Almost surely, 2^21520705 is an apocalyptic number.

It is an amenable number.

21520705 is a deficient number, since it is larger than the sum of its proper divisors (4304147).

21520705 is an equidigital number, since it uses as much as digits as its factorization.

21520705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4304146.

The product of its (nonzero) digits is 700, while the sum is 22.

The square root of 21520705 is about 4639.0413880456. The cubic root of 21520705 is about 278.1541206726.

The spelling of 21520705 in words is "twenty-one million, five hundred twenty thousand, seven hundred five".