21705844 has 6 divisors (see below), whose sum is σ = 37985234. Its totient is φ = 10852920.

The previous prime is 21705839. The next prime is 21705863. The reversal of 21705844 is 44850712.

It can be written as a sum of positive squares in only one way, i.e., 21049744 + 656100 = 4588^2 + 810^2 .

It is a super-2 number, since 2×21705844² = 942287327504672, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2713227 + ... + 2713234.

Almost surely, 2^21705844 is an apocalyptic number.

It is an amenable number.

21705844 is a deficient number, since it is larger than the sum of its proper divisors (16279390).

21705844 is a wasteful number, since it uses less digits than its factorization.

21705844 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5426465 (or 5426463 counting only the distinct ones).

The product of its (nonzero) digits is 8960, while the sum is 31.

The square root of 21705844 is about 4658.9531012879. The cubic root of 21705844 is about 278.9494819099.

The spelling of 21705844 in words is "twenty-one million, seven hundred five thousand, eight hundred forty-four".