687661 has 8 divisors (see below), whose sum is σ = 747320. Its totient is φ = 632736.

The previous prime is 687647. The next prime is 687679. The reversal of 687661 is 166786.

It can be written as a sum of positive squares in 4 ways, for example, as 447561 + 240100 = 669^2 + 490^2 .

It is not a de Polignac number, because 687661 - 2¹¹ = 685613 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (687641) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2041 + ... + 2353.

It is an arithmetic number, because the mean of its divisors is an integer number (93415).

2⁶⁸⁷⁶⁶¹ is an apocalyptic number.

It is an amenable number.

687661 is a deficient number, since it is larger than the sum of its proper divisors (59659).

687661 is an equidigital number, since it uses as much as digits as its factorization.

687661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 352 (or 326 counting only the distinct ones).

The product of its digits is 12096, while the sum is 34.

The square root of 687661 is about 829.2532785585. The cubic root of 687661 is about 88.2655973737.

The spelling of 687661 in words is "six hundred eighty-seven thousand, six hundred sixty-one".