21616321 has 4 divisors (see below), whose sum is σ = 21625812. Its totient is φ = 21606832.

The previous prime is 21616303. The next prime is 21616327. The reversal of 21616321 is 12361612.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 1185921 + 20430400 = 1089^2 + 4520^2 .

It is a cyclic number.

It is not a de Polignac number, because 21616321 - 2⁹ = 21615809 is a prime.

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

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21616292 and 21616301.

It is not an unprimeable number, because it can be changed into a prime (21616327) 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, 951 + ... + 6643.

It is an arithmetic number, because the mean of its divisors is an integer number (5406453).

Almost surely, 2^21616321 is an apocalyptic number.

It is an amenable number.

21616321 is a deficient number, since it is larger than the sum of its proper divisors (9491).

21616321 is an equidigital number, since it uses as much as digits as its factorization.

21616321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9490.

The product of its digits is 432, while the sum is 22.

The square root of 21616321 is about 4649.3355439245. The cubic root of 21616321 is about 278.5654562196.

Adding to 21616321 its reverse (12361612), we get a palindrome (33977933).

The spelling of 21616321 in words is "twenty-one million, six hundred sixteen thousand, three hundred twenty-one".