21458821 has 2 divisors, whose sum is σ = 21458822. Its totient is φ = 21458820.

The previous prime is 21458819. The next prime is 21458893. The reversal of 21458821 is 12885412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20802721 + 656100 = 4561^2 + 810^2 .

It is a cyclic number.

It is not a de Polignac number, because 21458821 - 2¹ = 21458819 is a prime.

Together with 21458819, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21458321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10729410 + 10729411.

It is an arithmetic number, because the mean of its divisors is an integer number (10729411).

Almost surely, 2^21458821 is an apocalyptic number.

It is an amenable number.

21458821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21458821 is an equidigital number, since it uses as much as digits as its factorization.

21458821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5120, while the sum is 31.

The square root of 21458821 is about 4632.3666737425. The cubic root of 21458821 is about 277.8872487575.

The spelling of 21458821 in words is "twenty-one million, four hundred fifty-eight thousand, eight hundred twenty-one".