21033809 has 2 divisors, whose sum is σ = 21033810. Its totient is φ = 21033808.

The previous prime is 21033781. The next prime is 21033823. The reversal of 21033809 is 90833012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12623809 + 8410000 = 3553^2 + 2900^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21033809 is a prime.

It is a super-2 number, since 2×21033809² = 884842242096962, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21036809) 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, 10516904 + 10516905.

It is an arithmetic number, because the mean of its divisors is an integer number (10516905).

Almost surely, 2^21033809 is an apocalyptic number.

It is an amenable number.

21033809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21033809 is an equidigital number, since it uses as much as digits as its factorization.

21033809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1296, while the sum is 26.

The square root of 21033809 is about 4586.2630757513. The cubic root of 21033809 is about 276.0403961386.

The spelling of 21033809 in words is "twenty-one million, thirty-three thousand, eight hundred nine".