685639681 has 4 divisors (see below), whose sum is σ = 721726000. Its totient is φ = 649553364.

The previous prime is 685639651. The next prime is 685639693. The reversal of 685639681 is 186936586.

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.

It is a cyclic number.

It is not a de Polignac number, because 685639681 - 2¹⁹ = 685115393 is a prime.

It is a super-2 number, since 2×685639681² = 940203544323563522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (685639651) 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, 18043131 + ... + 18043168.

It is an arithmetic number, because the mean of its divisors is an integer number (180431500).

Almost surely, 2^685639681 is an apocalyptic number.

It is an amenable number.

685639681 is a deficient number, since it is larger than the sum of its proper divisors (36086319).

685639681 is a wasteful number, since it uses less digits than its factorization.

685639681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36086318.

The product of its digits is 1866240, while the sum is 52.

The square root of 685639681 is about 26184.7222822775. The cubic root of 685639681 is about 881.7902951310.

The spelling of 685639681 in words is "six hundred eighty-five million, six hundred thirty-nine thousand, six hundred eighty-one".