21505223 has 4 divisors (see below), whose sum is σ = 21718248. Its totient is φ = 21292200.

The previous prime is 21505219. The next prime is 21505241. The reversal of 21505223 is 32250512.

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 21505223 - 2² = 21505219 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21505195 and 21505204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505243) 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, 106361 + ... + 106562.

It is an arithmetic number, because the mean of its divisors is an integer number (5429562).

Almost surely, 2^21505223 is an apocalyptic number.

21505223 is a deficient number, since it is larger than the sum of its proper divisors (213025).

21505223 is a wasteful number, since it uses less digits than its factorization.

21505223 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213024.

The product of its (nonzero) digits is 600, while the sum is 20.

The square root of 21505223 is about 4637.3724241212. The cubic root of 21505223 is about 278.0874032923.

Adding to 21505223 its reverse (32250512), we get a palindrome (53755735).

The spelling of 21505223 in words is "twenty-one million, five hundred five thousand, two hundred twenty-three".