21644705 has 16 divisors (see below), whose sum is σ = 27734400. Its totient is φ = 16168320.

The previous prime is 21644687. The next prime is 21644713. The reversal of 21644705 is 50744612.

It is not a de Polignac number, because 21644705 - 2⁶ = 21644641 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5141 + ... + 8349.

It is an arithmetic number, because the mean of its divisors is an integer number (1733400).

Almost surely, 2^21644705 is an apocalyptic number.

It is an amenable number.

21644705 is a deficient number, since it is larger than the sum of its proper divisors (6089695).

21644705 is a wasteful number, since it uses less digits than its factorization.

21644705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3304.

The product of its (nonzero) digits is 6720, while the sum is 29.

The square root of 21644705 is about 4652.3870217341. The cubic root of 21644705 is about 278.6873293122.

The spelling of 21644705 in words is "twenty-one million, six hundred forty-four thousand, seven hundred five".