684657781 has 4 divisors (see below), whose sum is σ = 708266700. Its totient is φ = 661048864.

The previous prime is 684657773. The next prime is 684657817. The reversal of 684657781 is 187756486.

684657781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 187756486 = 2 ⋅93878243.

It can be written as a sum of positive squares in 2 ways, for example, as 220255281 + 464402500 = 14841^2 + 21550^2 .

It is a cyclic number.

It is not a de Polignac number, because 684657781 - 2³ = 684657773 is a prime.

It is a super-2 number, since 2×684657781² = 937512554167687922, 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 (684657751) 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, 11804416 + ... + 11804473.

It is an arithmetic number, because the mean of its divisors is an integer number (177066675).

Almost surely, 2^684657781 is an apocalyptic number.

It is an amenable number.

684657781 is a deficient number, since it is larger than the sum of its proper divisors (23608919).

684657781 is a wasteful number, since it uses less digits than its factorization.

684657781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23608918.

The product of its digits is 2257920, while the sum is 52.

The square root of 684657781 is about 26165.9660819164. The cubic root of 684657781 is about 881.3691587040.

The spelling of 684657781 in words is "six hundred eighty-four million, six hundred fifty-seven thousand, seven hundred eighty-one".