21687805 has 4 divisors (see below), whose sum is σ = 26025372. Its totient is φ = 17350240.

The previous prime is 21687803. The next prime is 21687857. The reversal of 21687805 is 50878612.

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 11689561 + 9998244 = 3419^2 + 3162^2 .

It is not a de Polignac number, because 21687805 - 2¹ = 21687803 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21687803) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2168776 + ... + 2168785.

It is an arithmetic number, because the mean of its divisors is an integer number (6506343).

Almost surely, 2^21687805 is an apocalyptic number.

It is an amenable number.

21687805 is a deficient number, since it is larger than the sum of its proper divisors (4337567).

21687805 is an equidigital number, since it uses as much as digits as its factorization.

21687805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4337566.

The product of its (nonzero) digits is 26880, while the sum is 37.

The square root of 21687805 is about 4657.0167489499. The cubic root of 21687805 is about 278.8721853023.

The spelling of 21687805 in words is "twenty-one million, six hundred eighty-seven thousand, eight hundred five".