691687 has 2 divisors, whose sum is σ = 691688. Its totient is φ = 691686.

The previous prime is 691681. The next prime is 691693. The reversal of 691687 is 786196.

It is a balanced prime because it is at equal distance from previous prime (691681) and next prime (691693).

It is a cyclic number.

It is not a de Polignac number, because 691687 - 2¹⁵ = 658919 is a prime.

It is a Chen prime.

691687 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (691681) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345843 + 345844.

It is an arithmetic number, because the mean of its divisors is an integer number (345844).

2⁶⁹¹⁶⁸⁷ is an apocalyptic number.

691687 is a deficient number, since it is larger than the sum of its proper divisors (1).

691687 is an equidigital number, since it uses as much as digits as its factorization.

691687 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18144, while the sum is 37.

The square root of 691687 is about 831.6772210419. The cubic root of 691687 is about 88.4375164088.

It can be divided in two parts, 691 and 687, that added together give a triangular number (1378 = T₅₂).

The spelling of 691687 in words is "six hundred ninety-one thousand, six hundred eighty-seven".