2640809 has 4 divisors (see below), whose sum is σ = 2650116. Its totient is φ = 2631504.

The previous prime is 2640779. The next prime is 2640821. The reversal of 2640809 is 9080462.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 9080462 = 2 ⋅4540231.

It can be written as a sum of positive squares in 2 ways, for example, as 1968409 + 672400 = 1403^2 + 820^2 .

It is a cyclic number.

It is not a de Polignac number, because 2640809 - 2¹² = 2636713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2640889) 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, 4214 + ... + 4799.

It is an arithmetic number, because the mean of its divisors is an integer number (662529).

2^2640809 is an apocalyptic number.

It is an amenable number.

2640809 is a deficient number, since it is larger than the sum of its proper divisors (9307).

2640809 is an equidigital number, since it uses as much as digits as its factorization.

2640809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9306.

The product of its (nonzero) digits is 3456, while the sum is 29.

The square root of 2640809 is about 1625.0566143984. The cubic root of 2640809 is about 138.2225806645. Note that the first 3 decimals are identical.

The spelling of 2640809 in words is "two million, six hundred forty thousand, eight hundred nine".