661688 has 16 divisors (see below), whose sum is σ = 1253880. Its totient is φ = 327328.

The previous prime is 661679. The next prime is 661697. The reversal of 661688 is 886166.

It is an interprime number because it is at equal distance from previous prime (661679) and next prime (661697).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 470 + ... + 1242.

2⁶⁶¹⁶⁸⁸ is an apocalyptic number.

It is an amenable number.

661688 is a deficient number, since it is larger than the sum of its proper divisors (592192).

661688 is a wasteful number, since it uses less digits than its factorization.

661688 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 886 (or 882 counting only the distinct ones).

The product of its digits is 13824, while the sum is 35.

The square root of 661688 is about 813.4420692342. The cubic root of 661688 is about 87.1400395808.

The spelling of 661688 in words is "six hundred sixty-one thousand, six hundred eighty-eight".