1991864 has 16 divisors (see below), whose sum is σ = 4268400. Its totient is φ = 853632.

The previous prime is 1991863. The next prime is 1991879. The reversal of 1991864 is 4681991.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991861) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 17729 + ... + 17840.

It is an arithmetic number, because the mean of its divisors is an integer number (266775).

2^1991864 is an apocalyptic number.

1991864 is a gapful number since it is divisible by the number (14) formed by its first and last digit.

It is an amenable number.

1991864 is an abundant number, since it is smaller than the sum of its proper divisors (2276536).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1991864 is a wasteful number, since it uses less digits than its factorization.

1991864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35582 (or 35578 counting only the distinct ones).

The product of its digits is 15552, while the sum is 38.

The square root of 1991864 is about 1411.3341206107. The cubic root of 1991864 is about 125.8210275039.

The spelling of 1991864 in words is "one million, nine hundred ninety-one thousand, eight hundred sixty-four".