1991905 has 16 divisors (see below), whose sum is σ = 2515968. Its totient is φ = 1512000.

The previous prime is 1991893. The next prime is 1991911. The reversal of 1991905 is 5091991.

It is a de Polignac number, because none of the positive numbers 2^k-1991905 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10915 + ... + 11095.

It is an arithmetic number, because the mean of its divisors is an integer number (157248).

2^1991905 is an apocalyptic number.

It is an amenable number.

1991905 is a deficient number, since it is larger than the sum of its proper divisors (524063).

1991905 is a wasteful number, since it uses less digits than its factorization.

1991905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 288.

The product of its (nonzero) digits is 3645, while the sum is 34.

The square root of 1991905 is about 1411.3486457995. The cubic root of 1991905 is about 125.8218907869.

The spelling of 1991905 in words is "one million, nine hundred ninety-one thousand, nine hundred five".