21708621 has 32 divisors (see below), whose sum is σ = 36940800. Its totient is φ = 12461040.

The previous prime is 21708611. The next prime is 21708623. The reversal of 21708621 is 12680712.

It is not a de Polignac number, because 21708621 - 2¹⁵ = 21675853 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21708623) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 3720 + ... + 7566.

It is an arithmetic number, because the mean of its divisors is an integer number (1154400).

Almost surely, 2^21708621 is an apocalyptic number.

It is an amenable number.

21708621 is a deficient number, since it is larger than the sum of its proper divisors (15232179).

21708621 is a wasteful number, since it uses less digits than its factorization.

21708621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3886 (or 3880 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21708621 is about 4659.2511200836. The cubic root of 21708621 is about 278.9613774725.

The spelling of 21708621 in words is "twenty-one million, seven hundred eight thousand, six hundred twenty-one".