21509223 has 4 divisors (see below), whose sum is σ = 28678968. Its totient is φ = 14339480.

The previous prime is 21509207. The next prime is 21509227. The reversal of 21509223 is 32290512.

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 21509223 - 2⁴ = 21509207 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21509193 and 21509202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21509227) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3584868 + ... + 3584873.

It is an arithmetic number, because the mean of its divisors is an integer number (7169742).

Almost surely, 2^21509223 is an apocalyptic number.

21509223 is a deficient number, since it is larger than the sum of its proper divisors (7169745).

21509223 is an equidigital number, since it uses as much as digits as its factorization.

21509223 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7169744.

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21509223 is about 4637.8036827792. The cubic root of 21509223 is about 278.1046437654.

Adding to 21509223 its reverse (32290512), we get a palindrome (53799735).

The spelling of 21509223 in words is "twenty-one million, five hundred nine thousand, two hundred twenty-three".