21513223 has 4 divisors (see below), whose sum is σ = 21526848. Its totient is φ = 21499600.

The previous prime is 21513209. The next prime is 21513227. The reversal of 21513223 is 32231512.

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-21513223 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21513223.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21513227) 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, 4078 + ... + 7723.

It is an arithmetic number, because the mean of its divisors is an integer number (5381712).

Almost surely, 2^21513223 is an apocalyptic number.

21513223 is a deficient number, since it is larger than the sum of its proper divisors (13625).

21513223 is a wasteful number, since it uses less digits than its factorization.

21513223 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13624.

The product of its digits is 360, while the sum is 19.

The square root of 21513223 is about 4638.2349013391. The cubic root of 21513223 is about 278.1218821011.

Adding to 21513223 its reverse (32231512), we get a palindrome (53744735).

It can be divided in two parts, 21513 and 223, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 21513223 in words is "twenty-one million, five hundred thirteen thousand, two hundred twenty-three".