21705867 has 8 divisors (see below), whose sum is σ = 32156880. Its totient is φ = 14470560.

The previous prime is 21705863. The next prime is 21705883. The reversal of 21705867 is 76850712.

21705867 is a `hidden beast` number, since 2 + 1 + 70 + 586 + 7 = 666.

It is not a de Polignac number, because 21705867 - 2² = 21705863 is a prime.

It is a super-2 number, since 2×21705867² = 942289324443378, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21705863) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 401934 + ... + 401987.

It is an arithmetic number, because the mean of its divisors is an integer number (4019610).

Almost surely, 2^21705867 is an apocalyptic number.

21705867 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21705867 is a deficient number, since it is larger than the sum of its proper divisors (10451013).

21705867 is an equidigital number, since it uses as much as digits as its factorization.

21705867 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 803930 (or 803924 counting only the distinct ones).

The product of its (nonzero) digits is 23520, while the sum is 36.

The square root of 21705867 is about 4658.9555696529. The cubic root of 21705867 is about 278.9495804369.

The spelling of 21705867 in words is "twenty-one million, seven hundred five thousand, eight hundred sixty-seven".