1991689 has 4 divisors (see below), whose sum is σ = 2276224. Its totient is φ = 1707156.

The previous prime is 1991681. The next prime is 1991707. The reversal of 1991689 is 9861991.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1991689 - 2³ = 1991681 is a prime.

It is a Duffinian number.

1991689 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (1991681) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 142257 + ... + 142270.

It is an arithmetic number, because the mean of its divisors is an integer number (569056).

2^1991689 is an apocalyptic number.

It is an amenable number.

1991689 is a deficient number, since it is larger than the sum of its proper divisors (284535).

1991689 is an equidigital number, since it uses as much as digits as its factorization.

1991689 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 284534.

The product of its digits is 34992, while the sum is 43.

The square root of 1991689 is about 1411.2721211730. The cubic root of 1991689 is about 125.8173426264.

The spelling of 1991689 in words is "one million, nine hundred ninety-one thousand, six hundred eighty-nine".