21108321 has 12 divisors (see below), whose sum is σ = 32835348. Its totient is φ = 12989664.

The previous prime is 21108301. The next prime is 21108323. The reversal of 21108321 is 12380112.

It can be written as a sum of positive squares in 2 ways, for example, as 1527696 + 19580625 = 1236^2 + 4425^2 .

It is not a de Polignac number, because 21108321 - 2¹³ = 21100129 is a prime.

It is a super-2 number, since 2×21108321² = 891122430878082, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21108294 and 21108303.

It is not an unprimeable number, because it can be changed into a prime (21108323) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 90090 + ... + 90323.

It is an arithmetic number, because the mean of its divisors is an integer number (2736279).

Almost surely, 2^21108321 is an apocalyptic number.

It is an amenable number.

21108321 is a deficient number, since it is larger than the sum of its proper divisors (11727027).

21108321 is a wasteful number, since it uses less digits than its factorization.

21108321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 180432 (or 180429 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21108321 is about 4594.3792834288. The cubic root of 21108321 is about 276.3659685224.

Adding to 21108321 its reverse (12380112), we get a palindrome (33488433).

The spelling of 21108321 in words is "twenty-one million, one hundred eight thousand, three hundred twenty-one".