21432809 has 2 divisors, whose sum is σ = 21432810. Its totient is φ = 21432808.

The previous prime is 21432793. The next prime is 21432821. The reversal of 21432809 is 90823412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19669225 + 1763584 = 4435^2 + 1328^2 .

It is a cyclic number.

It is not a de Polignac number, because 21432809 - 2⁴ = 21432793 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21432409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10716404 + 10716405.

It is an arithmetic number, because the mean of its divisors is an integer number (10716405).

Almost surely, 2^21432809 is an apocalyptic number.

It is an amenable number.

21432809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21432809 is an equidigital number, since it uses as much as digits as its factorization.

21432809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3456, while the sum is 29.

The square root of 21432809 is about 4629.5581862636. The cubic root of 21432809 is about 277.7749200358.

The spelling of 21432809 in words is "twenty-one million, four hundred thirty-two thousand, eight hundred nine".