20681809 has 4 divisors (see below), whose sum is σ = 21898404. Its totient is φ = 19465216.

The previous prime is 20681777. The next prime is 20681813. The reversal of 20681809 is 90818602.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6969600 + 13712209 = 2640^2 + 3703^2 .

It is a cyclic number.

It is not a de Polignac number, because 20681809 - 2⁵ = 20681777 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20681879) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 608272 + ... + 608305.

It is an arithmetic number, because the mean of its divisors is an integer number (5474601).

Almost surely, 2^20681809 is an apocalyptic number.

It is an amenable number.

20681809 is a deficient number, since it is larger than the sum of its proper divisors (1216595).

20681809 is a wasteful number, since it uses less digits than its factorization.

20681809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1216594.

The product of its (nonzero) digits is 6912, while the sum is 34.

The square root of 20681809 is about 4547.7256953339. The cubic root of 20681809 is about 274.4918837728.

The spelling of 20681809 in words is "twenty million, six hundred eighty-one thousand, eight hundred nine".