1855991 has 4 divisors (see below), whose sum is σ = 1863312. Its totient is φ = 1848672.

The previous prime is 1855981. The next prime is 1855993. The reversal of 1855991 is 1995581.

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 1855991 - 2⁶ = 1855927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1855993) 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, 3266 + ... + 3791.

It is an arithmetic number, because the mean of its divisors is an integer number (465828).

2^1855991 is an apocalyptic number.

1855991 is a deficient number, since it is larger than the sum of its proper divisors (7321).

1855991 is an equidigital number, since it uses as much as digits as its factorization.

1855991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7320.

The product of its digits is 16200, while the sum is 38.

The square root of 1855991 is about 1362.3476061564. The cubic root of 1855991 is about 122.8924743859.

The spelling of 1855991 in words is "one million, eight hundred fifty-five thousand, nine hundred ninety-one".