21223521 has 18 divisors (see below), whose sum is σ = 33698210. Its totient is φ = 12862080.

The previous prime is 21223519. The next prime is 21223583. The reversal of 21223521 is 12532212.

It can be written as a sum of positive squares in only one way, i.e., 12006225 + 9217296 = 3465^2 + 3036^2 .

It is not a de Polignac number, because 21223521 - 2¹ = 21223519 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21223494 and 21223503.

It is not an unprimeable number, because it can be changed into a prime (21223511) 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 17 ways as a sum of consecutive naturals, for example, 8656 + ... + 10833.

Almost surely, 2^21223521 is an apocalyptic number.

It is an amenable number.

21223521 is a deficient number, since it is larger than the sum of its proper divisors (12474689).

21223521 is a wasteful number, since it uses less digits than its factorization.

21223521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19517 (or 19503 counting only the distinct ones).

The product of its digits is 240, while the sum is 18.

The square root of 21223521 is about 4606.8992825978. The cubic root of 21223521 is about 276.8678182654.

Adding to 21223521 its reverse (12532212), we get a palindrome (33755733).

The spelling of 21223521 in words is "twenty-one million, two hundred twenty-three thousand, five hundred twenty-one".