20802809 has 2 divisors, whose sum is σ = 20802810. Its totient is φ = 20802808.

The previous prime is 20802779. The next prime is 20802823. The reversal of 20802809 is 90820802.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20475625 + 327184 = 4525^2 + 572^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20802809 is a prime.

It is not a weakly prime, because it can be changed into another prime (20802839) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10401404 + 10401405.

It is an arithmetic number, because the mean of its divisors is an integer number (10401405).

Almost surely, 2^20802809 is an apocalyptic number.

It is an amenable number.

20802809 is a deficient number, since it is larger than the sum of its proper divisors (1).

20802809 is an equidigital number, since it uses as much as digits as its factorization.

20802809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 20802809 is about 4561.0096469970. The cubic root of 20802809 is about 275.0261528846.

The spelling of 20802809 in words is "twenty million, eight hundred two thousand, eight hundred nine".