21066809 has 2 divisors, whose sum is σ = 21066810. Its totient is φ = 21066808.

The previous prime is 21066797. The next prime is 21066817. The reversal of 21066809 is 90866012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11580409 + 9486400 = 3403^2 + 3080^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21066809 is a prime.

It is not a weakly prime, because it can be changed into another prime (21066109) 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, 10533404 + 10533405.

It is an arithmetic number, because the mean of its divisors is an integer number (10533405).

Almost surely, 2^21066809 is an apocalyptic number.

It is an amenable number.

21066809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21066809 is an equidigital number, since it uses as much as digits as its factorization.

21066809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5184, while the sum is 32.

The square root of 21066809 is about 4589.8593660373. The cubic root of 21066809 is about 276.1846808841.

The spelling of 21066809 in words is "twenty-one million, sixty-six thousand, eight hundred nine".