21721863 has 8 divisors (see below), whose sum is σ = 28984176. Its totient is φ = 14470400.

The previous prime is 21721831. The next prime is 21721871. The reversal of 21721863 is 36812712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21721863 - 2⁵ = 21721831 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21721863.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21721813) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 5623 + ... + 8663.

It is an arithmetic number, because the mean of its divisors is an integer number (3623022).

Almost surely, 2^21721863 is an apocalyptic number.

21721863 is a deficient number, since it is larger than the sum of its proper divisors (7262313).

21721863 is a wasteful number, since it uses less digits than its factorization.

21721863 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5425.

The product of its digits is 4032, while the sum is 30.

The square root of 21721863 is about 4660.6719472625. The cubic root of 21721863 is about 279.0180869815.

The spelling of 21721863 in words is "twenty-one million, seven hundred twenty-one thousand, eight hundred sixty-three".