1991785644 has 18 divisors (see below), whose sum is σ = 5034791580. Its totient is φ = 663928536.

The previous prime is 1991785643. The next prime is 1991785657. The reversal of 1991785644 is 4465871991.

1991785644 is a `hidden beast` number, since 1 + 9 + 9 + 1 + 78 + 564 + 4 = 666.

It is a tau number, because it is divible by the number of its divisors (18).

It is not an unprimeable number, because it can be changed into a prime (1991785643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 27663654 + ... + 27663725.

Almost surely, 2^1991785644 is an apocalyptic number.

It is an amenable number.

1991785644 is an abundant number, since it is smaller than the sum of its proper divisors (3043005936).

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

1991785644 is a wasteful number, since it uses less digits than its factorization.

1991785644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55327389 (or 55327384 counting only the distinct ones).

The product of its digits is 2177280, while the sum is 54.

The square root of 1991785644 is about 44629.4257637268. The cubic root of 1991785644 is about 1258.1937763195.

The spelling of 1991785644 in words is "one billion, nine hundred ninety-one million, seven hundred eighty-five thousand, six hundred forty-four".