21686705 has 4 divisors (see below), whose sum is σ = 26024052. Its totient is φ = 17349360.

The previous prime is 21686671. The next prime is 21686741. The reversal of 21686705 is 50768612.

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 15295921 + 6390784 = 3911^2 + 2528^2 .

It is not a de Polignac number, because 21686705 - 2⁸ = 21686449 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2168666 + ... + 2168675.

It is an arithmetic number, because the mean of its divisors is an integer number (6506013).

Almost surely, 2^21686705 is an apocalyptic number.

It is an amenable number.

21686705 is a deficient number, since it is larger than the sum of its proper divisors (4337347).

21686705 is an equidigital number, since it uses as much as digits as its factorization.

21686705 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4337346.

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 21686705 is about 4656.8986460948. The cubic root of 21686705 is about 278.8674704470.

The spelling of 21686705 in words is "twenty-one million, six hundred eighty-six thousand, seven hundred five".