21216321 has 12 divisors (see below), whose sum is σ = 35023872. Its totient is φ = 12123576.

The previous prime is 21216263. The next prime is 21216361. The reversal of 21216321 is 12361212.

It is not a de Polignac number, because 21216321 - 2⁷ = 21216193 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a junction number, because it is equal to n+sod(n) for n = 21216294 and 21216303.

It is not an unprimeable number, because it can be changed into a prime (21216361) 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 11 ways as a sum of consecutive naturals, for example, 168321 + ... + 168446.

It is an arithmetic number, because the mean of its divisors is an integer number (2918656).

Almost surely, 2^21216321 is an apocalyptic number.

21216321 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21216321 is a deficient number, since it is larger than the sum of its proper divisors (13807551).

21216321 is a wasteful number, since it uses less digits than its factorization.

21216321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 336780 (or 336777 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21216321 is about 4606.1177796491. The cubic root of 21216321 is about 276.8365059342.

Adding to 21216321 its reverse (12361212), we get a palindrome (33577533).

The spelling of 21216321 in words is "twenty-one million, two hundred sixteen thousand, three hundred twenty-one".