1688991 has 4 divisors (see below), whose sum is σ = 2251992. Its totient is φ = 1125992.

The previous prime is 1688987. The next prime is 1689031. The reversal of 1688991 is 1998861.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1688991 - 2² = 1688987 is a prime.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1688971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 281496 + ... + 281501.

It is an arithmetic number, because the mean of its divisors is an integer number (562998).

2^1688991 is an apocalyptic number.

1688991 is a deficient number, since it is larger than the sum of its proper divisors (563001).

1688991 is an equidigital number, since it uses as much as digits as its factorization.

1688991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 563000.

The product of its digits is 31104, while the sum is 42.

The square root of 1688991 is about 1299.6118651351. The cubic root of 1688991 is about 119.0901325012.

The spelling of 1688991 in words is "one million, six hundred eighty-eight thousand, nine hundred ninety-one".