21223021 has 4 divisors (see below), whose sum is σ = 22471452. Its totient is φ = 19974592.

The previous prime is 21223009. The next prime is 21223051. The reversal of 21223021 is 12032212.

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

It can be written as a sum of positive squares in 2 ways, for example, as 11526025 + 9696996 = 3395^2 + 3114^2 .

It is not a de Polignac number, because 21223021 - 2¹⁷ = 21091949 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21222992 and 21223010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21223051) 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, 624190 + ... + 624223.

It is an arithmetic number, because the mean of its divisors is an integer number (5617863).

Almost surely, 2^21223021 is an apocalyptic number.

It is an amenable number.

21223021 is a deficient number, since it is larger than the sum of its proper divisors (1248431).

21223021 is a wasteful number, since it uses less digits than its factorization.

21223021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1248430.

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21223021 is about 4606.8450158433. The cubic root of 21223021 is about 276.8656440268.

Adding to 21223021 its reverse (12032212), we get a palindrome (33255233).

The spelling of 21223021 in words is "twenty-one million, two hundred twenty-three thousand, twenty-one".