691688 has 8 divisors (see below), whose sum is σ = 1296930. Its totient is φ = 345840.

The previous prime is 691687. The next prime is 691693. The reversal of 691688 is 886196.

691688 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 357604 + 334084 = 598^2 + 578^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is not an unprimeable number, because it can be changed into a prime (691681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 43223 + ... + 43238.

2⁶⁹¹⁶⁸⁸ is an apocalyptic number.

It is an amenable number.

691688 is a deficient number, since it is larger than the sum of its proper divisors (605242).

691688 is a wasteful number, since it uses less digits than its factorization.

691688 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86467 (or 86463 counting only the distinct ones).

The product of its digits is 20736, while the sum is 38.

The square root of 691688 is about 831.6778222365. The cubic root of 691688 is about 88.4375590280.

The spelling of 691688 in words is "six hundred ninety-one thousand, six hundred eighty-eight".