6785811391681 has 9 divisors (see below), whose sum is σ = 7893720177699. Its totient is φ = 5816394134544.

The previous prime is 6785811391663. The next prime is 6785811391693. The reversal of 6785811391681 is 1861931185876.

The square root of 6785811391681 is 2604959.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 2968539473025 + 3817271918656 = 1722945^2 + 1953784^2 .

It is not a de Polignac number, because 6785811391681 - 2⁵ = 6785811391649 is a prime.

It is a super-2 number, since 2×6785811391681² (a number of 26 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6785811391661) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 18048645 + ... + 18420781.

Almost surely, 2^{6785811391681} is an apocalyptic number.

6785811391681 is the 2604959-th square number.

6785811391681 is the 1302480-th centered octagonal number.

It is an amenable number.

6785811391681 is a deficient number, since it is larger than the sum of its proper divisors (1107908786018).

6785811391681 is an frugal number, since it uses more digits than its factorization.

6785811391681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 744288 (or 372144 counting only the distinct ones).

The product of its digits is 17418240, while the sum is 64.

Multiplying 6785811391681 by its sum of digits (64), we get a square (434291929067584 = 20839672²).

The spelling of 6785811391681 in words is "six trillion, seven hundred eighty-five billion, eight hundred eleven million, three hundred ninety-one thousand, six hundred eighty-one".