1991559 has 4 divisors (see below), whose sum is σ = 2655416. Its totient is φ = 1327704.

The previous prime is 1991551. The next prime is 1991573. The reversal of 1991559 is 9551991.

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

It is not a de Polignac number, because 1991559 - 2³ = 1991551 is a prime.

It is an Ulam number.

It is a D-number.

It is a Duffinian number.

It is a zygodrome in base 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991551) 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, 331924 + ... + 331929.

It is an arithmetic number, because the mean of its divisors is an integer number (663854).

2^1991559 is an apocalyptic number.

1991559 is a deficient number, since it is larger than the sum of its proper divisors (663857).

1991559 is an equidigital number, since it uses as much as digits as its factorization.

1991559 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 663856.

The product of its digits is 18225, while the sum is 39.

The square root of 1991559 is about 1411.2260626845. The cubic root of 1991559 is about 125.8146051491.

The spelling of 1991559 in words is "one million, nine hundred ninety-one thousand, five hundred fifty-nine".