21702809 has 2 divisors, whose sum is σ = 21702810. Its totient is φ = 21702808.

The previous prime is 21702719. The next prime is 21702833. The reversal of 21702809 is 90820712.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18361225 + 3341584 = 4285^2 + 1828^2 .

It is a cyclic number.

It is not a de Polignac number, because 21702809 - 2¹² = 21698713 is a prime.

It is not a weakly prime, because it can be changed into another prime (21702859) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10851404 + 10851405.

It is an arithmetic number, because the mean of its divisors is an integer number (10851405).

Almost surely, 2^21702809 is an apocalyptic number.

It is an amenable number.

21702809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21702809 is an equidigital number, since it uses as much as digits as its factorization.

21702809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 21702809 is about 4658.6273729501. The cubic root of 21702809 is about 278.9364800176.

The spelling of 21702809 in words is "twenty-one million, seven hundred two thousand, eight hundred nine".