685509891 has 12 divisors (see below), whose sum is σ = 1004659656. Its totient is φ = 415460320.

The previous prime is 685509889. The next prime is 685509893. The reversal of 685509891 is 198905586.

It is an interprime number because it is at equal distance from previous prime (685509889) and next prime (685509893).

It is not a de Polignac number, because 685509891 - 2¹ = 685509889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (685509893) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 943866 + ... + 944591.

It is an arithmetic number, because the mean of its divisors is an integer number (83721638).

Almost surely, 2^685509891 is an apocalyptic number.

685509891 is a deficient number, since it is larger than the sum of its proper divisors (319149765).

685509891 is a wasteful number, since it uses less digits than its factorization.

685509891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1888482 (or 1888471 counting only the distinct ones).

The product of its (nonzero) digits is 777600, while the sum is 51.

The square root of 685509891 is about 26182.2438114078. The cubic root of 685509891 is about 881.7346513344.

The spelling of 685509891 in words is "six hundred eighty-five million, five hundred nine thousand, eight hundred ninety-one".