21221723 has 4 divisors (see below), whose sum is σ = 21739368. Its totient is φ = 20704080.

The previous prime is 21221693. The next prime is 21221731. The reversal of 21221723 is 32712212.

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 21221723 - 2⁸ = 21221467 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21221695 and 21221704.

It is not an unprimeable number, because it can be changed into a prime (21221743) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 258761 + ... + 258842.

It is an arithmetic number, because the mean of its divisors is an integer number (5434842).

Almost surely, 2^21221723 is an apocalyptic number.

21221723 is a deficient number, since it is larger than the sum of its proper divisors (517645).

21221723 is an equidigital number, since it uses as much as digits as its factorization.

21221723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 517644.

The product of its digits is 336, while the sum is 20.

The square root of 21221723 is about 4606.7041363647. The cubic root of 21221723 is about 276.8599995440.

Adding to 21221723 its reverse (32712212), we get a palindrome (53933935).

The spelling of 21221723 in words is "twenty-one million, two hundred twenty-one thousand, seven hundred twenty-three".