1991305 has 4 divisors (see below), whose sum is σ = 2389572. Its totient is φ = 1593040.

The previous prime is 1991293. The next prime is 1991351. The reversal of 1991305 is 5031991.

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

It can be written as a sum of positive squares in 2 ways, for example, as 1567504 + 423801 = 1252^2 + 651^2 .

It is not a de Polignac number, because 1991305 - 2⁷ = 1991177 is a prime.

It is a Duffinian number.

1991305 is a lucky number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 199126 + ... + 199135.

It is an arithmetic number, because the mean of its divisors is an integer number (597393).

2^1991305 is an apocalyptic number.

It is an amenable number.

1991305 is a deficient number, since it is larger than the sum of its proper divisors (398267).

1991305 is an equidigital number, since it uses as much as digits as its factorization.

1991305 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 398266.

The product of its (nonzero) digits is 1215, while the sum is 28.

The square root of 1991305 is about 1411.1360671459. The cubic root of 1991305 is about 125.8092561957.

The spelling of 1991305 in words is "one million, nine hundred ninety-one thousand, three hundred five".