21432821 has 2 divisors, whose sum is σ = 21432822. Its totient is φ = 21432820.

The previous prime is 21432809. The next prime is 21432833. The reversal of 21432821 is 12823412.

It is a happy number.

It is a balanced prime because it is at equal distance from previous prime (21432809) and next prime (21432833).

It can be written as a sum of positive squares in only one way, i.e., 19140625 + 2292196 = 4375^2 + 1514^2 .

It is a cyclic number.

It is not a de Polignac number, because 21432821 - 2²² = 17238517 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21432881) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10716410 + 10716411.

It is an arithmetic number, because the mean of its divisors is an integer number (10716411).

Almost surely, 2^21432821 is an apocalyptic number.

It is an amenable number.

21432821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21432821 is an equidigital number, since it uses as much as digits as its factorization.

21432821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 768, while the sum is 23.

The square root of 21432821 is about 4629.5594822834. The cubic root of 21432821 is about 277.7749718768.

The spelling of 21432821 in words is "twenty-one million, four hundred thirty-two thousand, eight hundred twenty-one".