21644321 has 2 divisors, whose sum is σ = 21644322. Its totient is φ = 21644320.

The previous prime is 21644309. The next prime is 21644339. The reversal of 21644321 is 12344612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16974400 + 4669921 = 4120^2 + 2161^2 .

It is a cyclic number.

It is not a de Polignac number, because 21644321 - 2⁶ = 21644257 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21644921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10822160 + 10822161.

It is an arithmetic number, because the mean of its divisors is an integer number (10822161).

Almost surely, 2^21644321 is an apocalyptic number.

It is an amenable number.

21644321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21644321 is an equidigital number, since it uses as much as digits as its factorization.

21644321 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1152, while the sum is 23.

The square root of 21644321 is about 4652.3457524135. The cubic root of 21644321 is about 278.6856812329.

Adding to 21644321 its reverse (12344612), we get a palindrome (33988933).

The spelling of 21644321 in words is "twenty-one million, six hundred forty-four thousand, three hundred twenty-one".