2687809781 has 4 divisors (see below), whose sum is σ = 2688051564. Its totient is φ = 2687568000.

The previous prime is 2687809777. The next prime is 2687809793. The reversal of 2687809781 is 1879087862.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1879087862 = 2 ⋅939543931.

It can be written as a sum of positive squares in 2 ways, for example, as 948085681 + 1739724100 = 30791^2 + 41710^2 .

It is a cyclic number.

It is not a de Polignac number, because 2687809781 - 2² = 2687809777 is a prime.

It is a super-2 number, since 2×2687809781² = 14448642837678535922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2687809681) 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, 103370 + ... + 126731.

It is an arithmetic number, because the mean of its divisors is an integer number (672012891).

Almost surely, 2^2687809781 is an apocalyptic number.

It is an amenable number.

2687809781 is a deficient number, since it is larger than the sum of its proper divisors (241783).

2687809781 is a wasteful number, since it uses less digits than its factorization.

2687809781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 241782.

The product of its (nonzero) digits is 2709504, while the sum is 56.

The square root of 2687809781 is about 51844.0910904994. The cubic root of 2687809781 is about 1390.3778592487.

The spelling of 2687809781 in words is "two billion, six hundred eighty-seven million, eight hundred nine thousand, seven hundred eighty-one".