991779 has 8 divisors (see below), whose sum is σ = 1327872. Its totient is φ = 658440.

The previous prime is 991777. The next prime is 991811. The reversal of 991779 is 977199.

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

It is not a de Polignac number, because 991779 - 2¹ = 991777 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 991779.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991779.

It is not an unprimeable number, because it can be changed into a prime (991777) 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, 402 + ... + 1464.

It is an arithmetic number, because the mean of its divisors is an integer number (165984).

2⁹⁹¹⁷⁷⁹ is an apocalyptic number.

991779 is a deficient number, since it is larger than the sum of its proper divisors (336093).

991779 is a wasteful number, since it uses less digits than its factorization.

991779 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1377.

The product of its digits is 35721, while the sum is 42.

The square root of 991779 is about 995.8810169895. The cubic root of 991779 is about 99.7252122754.

It can be divided in two parts, 991 and 779, that added together give a triangular number (1770 = T₅₉).

The spelling of 991779 in words is "nine hundred ninety-one thousand, seven hundred seventy-nine".