21368821 has 2 divisors, whose sum is σ = 21368822. Its totient is φ = 21368820.

The previous prime is 21368803. The next prime is 21368843. The reversal of 21368821 is 12886312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19704721 + 1664100 = 4439^2 + 1290^2 .

It is a cyclic number.

It is not a de Polignac number, because 21368821 - 2⁹ = 21368309 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21368801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10684410 + 10684411.

It is an arithmetic number, because the mean of its divisors is an integer number (10684411).

Almost surely, 2^21368821 is an apocalyptic number.

It is an amenable number.

21368821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21368821 is an equidigital number, since it uses as much as digits as its factorization.

21368821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4608, while the sum is 31.

The square root of 21368821 is about 4622.6422098190. The cubic root of 21368821 is about 277.4982106315.

The spelling of 21368821 in words is "twenty-one million, three hundred sixty-eight thousand, eight hundred twenty-one".