21036809 has 2 divisors, whose sum is σ = 21036810. Its totient is φ = 21036808.

The previous prime is 21036797. The next prime is 21036811. The reversal of 21036809 is 90863012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11868025 + 9168784 = 3445^2 + 3028^2 .

It is a cyclic number.

It is not a de Polignac number, because 21036809 - 2²⁰ = 19988233 is a prime.

Together with 21036811, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21036889) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10518404 + 10518405.

It is an arithmetic number, because the mean of its divisors is an integer number (10518405).

Almost surely, 2^21036809 is an apocalyptic number.

It is an amenable number.

21036809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21036809 is an equidigital number, since it uses as much as digits as its factorization.

21036809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2592, while the sum is 29.

The square root of 21036809 is about 4586.5901277529. The cubic root of 21036809 is about 276.0535191670.

The spelling of 21036809 in words is "twenty-one million, thirty-six thousand, eight hundred nine".