1991081124 has 18 divisors (see below), whose sum is σ = 5033010710. Its totient is φ = 663693696.

The previous prime is 1991081093. The next prime is 1991081153. The reversal of 1991081124 is 4211801991.

It can be written as a sum of positive squares in only one way, i.e., 1285222500 + 705858624 = 35850^2 + 26568^2 .

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

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 55307809 = 1991081124 / (1 + 9 + 9 + 1 + 0 + 8 + 1 + 1 + 2 + 4).

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 27653869 + ... + 27653940.

Almost surely, 2^1991081124 is an apocalyptic number.

It is an amenable number.

1991081124 is an abundant number, since it is smaller than the sum of its proper divisors (3041929586).

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

1991081124 is a wasteful number, since it uses less digits than its factorization.

1991081124 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55307819 (or 55307814 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 36.

The square root of 1991081124 is about 44621.5320669293. The cubic root of 1991081124 is about 1258.0454124271.

The spelling of 1991081124 in words is "one billion, nine hundred ninety-one million, eighty-one thousand, one hundred twenty-four".