688661 has 2 divisors, whose sum is σ = 688662. Its totient is φ = 688660.

The previous prime is 688657. The next prime is 688669. The reversal of 688661 is 166886.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 481636 + 207025 = 694^2 + 455^2 .

It is a cyclic number.

It is not a de Polignac number, because 688661 - 2² = 688657 is a prime.

It is a Chen prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (688669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 344330 + 344331.

It is an arithmetic number, because the mean of its divisors is an integer number (344331).

2⁶⁸⁸⁶⁶¹ is an apocalyptic number.

It is an amenable number.

688661 is a deficient number, since it is larger than the sum of its proper divisors (1).

688661 is an equidigital number, since it uses as much as digits as its factorization.

688661 is an odious number, because the sum of its binary digits is odd.

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

The square root of 688661 is about 829.8560116068. The cubic root of 688661 is about 88.3083620724.

The spelling of 688661 in words is "six hundred eighty-eight thousand, six hundred sixty-one".