661689 has 24 divisors (see below), whose sum is σ = 1135680. Its totient is φ = 377136.

The previous prime is 661679. The next prime is 661697. The reversal of 661689 is 986166.

It is not a de Polignac number, because 661689 - 2⁴ = 661673 is a prime.

661689 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661679) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1507 + ... + 1895.

It is an arithmetic number, because the mean of its divisors is an integer number (47320).

2⁶⁶¹⁶⁸⁹ is an apocalyptic number.

It is an amenable number.

661689 is a deficient number, since it is larger than the sum of its proper divisors (473991).

661689 is an equidigital number, since it uses as much as digits as its factorization.

661689 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 411 (or 399 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 661689 is about 813.4426839059. The cubic root of 661689 is about 87.1400834786.

The spelling of 661689 in words is "six hundred sixty-one thousand, six hundred eighty-nine".