21208223 has 4 divisors (see below), whose sum is σ = 21221400. Its totient is φ = 21195048.

The previous prime is 21208183. The next prime is 21208259. The reversal of 21208223 is 32280212.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21208223 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21208195 and 21208204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21208423) 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, 3773 + ... + 7526.

It is an arithmetic number, because the mean of its divisors is an integer number (5305350).

Almost surely, 2^21208223 is an apocalyptic number.

21208223 is a deficient number, since it is larger than the sum of its proper divisors (13177).

21208223 is a wasteful number, since it uses less digits than its factorization.

21208223 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13176.

The product of its (nonzero) digits is 384, while the sum is 20.

The square root of 21208223 is about 4605.2386474536. The cubic root of 21208223 is about 276.8012797938.

Adding to 21208223 its reverse (32280212), we get a palindrome (53488435).

The spelling of 21208223 in words is "twenty-one million, two hundred eight thousand, two hundred twenty-three".