1991705 has 4 divisors (see below), whose sum is σ = 2390052. Its totient is φ = 1593360.

The previous prime is 1991681. The next prime is 1991707. The reversal of 1991705 is 5071991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5071991 = 827 ⋅6133.

It can be written as a sum of positive squares in 2 ways, for example, as 755161 + 1236544 = 869^2 + 1112^2 .

It is not a de Polignac number, because 1991705 - 2⁶ = 1991641 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991707) 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, 199166 + ... + 199175.

It is an arithmetic number, because the mean of its divisors is an integer number (597513).

2^1991705 is an apocalyptic number.

It is an amenable number.

1991705 is a deficient number, since it is larger than the sum of its proper divisors (398347).

1991705 is an equidigital number, since it uses as much as digits as its factorization.

1991705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 398346.

The product of its (nonzero) digits is 2835, while the sum is 32.

The square root of 1991705 is about 1411.2777898061. The cubic root of 1991705 is about 125.8176795384.

The spelling of 1991705 in words is "one million, nine hundred ninety-one thousand, seven hundred five".