19705809 has 4 divisors (see below), whose sum is σ = 26274416. Its totient is φ = 13137204.

The previous prime is 19705799. The next prime is 19705817. The reversal of 19705809 is 90850791.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 90850791 = 3 ⋅30283597.

It is a de Polignac number, because none of the positive numbers 2^k-19705809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19705859) 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, 3284299 + ... + 3284304.

It is an arithmetic number, because the mean of its divisors is an integer number (6568604).

Almost surely, 2^19705809 is an apocalyptic number.

It is an amenable number.

19705809 is a deficient number, since it is larger than the sum of its proper divisors (6568607).

19705809 is an equidigital number, since it uses as much as digits as its factorization.

19705809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6568606.

The product of its (nonzero) digits is 22680, while the sum is 39.

The square root of 19705809 is about 4439.1225484323. The cubic root of 19705809 is about 270.1042532930.

The spelling of 19705809 in words is "nineteen million, seven hundred five thousand, eight hundred nine".