1991081779 has 8 divisors (see below), whose sum is σ = 2085380640. Its totient is φ = 1897427136.

The previous prime is 1991081749. The next prime is 1991081783. The reversal of 1991081779 is 9771801991.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 1991081779 - 2⁵ = 1991081747 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991081749) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 154722 + ... + 167095.

It is an arithmetic number, because the mean of its divisors is an integer number (260672580).

Almost surely, 2^1991081779 is an apocalyptic number.

1991081779 is a deficient number, since it is larger than the sum of its proper divisors (94298861).

1991081779 is a wasteful number, since it uses less digits than its factorization.

1991081779 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 322109.

The product of its (nonzero) digits is 285768, while the sum is 52.

The square root of 1991081779 is about 44621.5394064346. The cubic root of 1991081779 is about 1258.0455503789.

The spelling of 1991081779 in words is "one billion, nine hundred ninety-one million, eighty-one thousand, seven hundred seventy-nine".