21721703 has 4 divisors (see below), whose sum is σ = 21740688. Its totient is φ = 21702720.

The previous prime is 21721621. The next prime is 21721717. The reversal of 21721703 is 30712712.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21721703 - 2¹⁴ = 21705319 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21721723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7658 + ... + 10103.

It is an arithmetic number, because the mean of its divisors is an integer number (5435172).

Almost surely, 2^21721703 is an apocalyptic number.

21721703 is a deficient number, since it is larger than the sum of its proper divisors (18985).

21721703 is a wasteful number, since it uses less digits than its factorization.

21721703 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18984.

The product of its (nonzero) digits is 588, while the sum is 23.

The square root of 21721703 is about 4660.6547823240. The cubic root of 21721703 is about 279.0174019113.

The spelling of 21721703 in words is "twenty-one million, seven hundred twenty-one thousand, seven hundred three".