1991779 has 2 divisors, whose sum is σ = 1991780. Its totient is φ = 1991778.

The previous prime is 1991761. The next prime is 1991797. The reversal of 1991779 is 9771991.

Together with next prime (1991797) it forms an Ormiston pair, because they use the same digits, order apart.

It is a balanced prime because it is at equal distance from previous prime (1991761) and next prime (1991797).

It is a cyclic number.

It is not a de Polignac number, because 1991779 - 2⁹ = 1991267 is a prime.

1991779 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (1991729) 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 as a sum of consecutive naturals, namely, 995889 + 995890.

It is an arithmetic number, because the mean of its divisors is an integer number (995890).

2^1991779 is an apocalyptic number.

1991779 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991779 is an equidigital number, since it uses as much as digits as its factorization.

1991779 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 35721, while the sum is 43.

The square root of 1991779 is about 1411.3040069383. The cubic root of 1991779 is about 125.8192377332.

The spelling of 1991779 in words is "one million, nine hundred ninety-one thousand, seven hundred seventy-nine".