1991797 has 2 divisors, whose sum is σ = 1991798. Its totient is φ = 1991796.

The previous prime is 1991779. The next prime is 1991819. The reversal of 1991797 is 7971991.

Together with previous prime (1991779) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1957201 + 34596 = 1399^2 + 186^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991797 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991707) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995898 + 995899.

It is an arithmetic number, because the mean of its divisors is an integer number (995899).

2^1991797 is an apocalyptic number.

It is an amenable number.

1991797 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991797 is an equidigital number, since it uses as much as digits as its factorization.

1991797 is an evil number, because the sum of its binary digits is even.

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

The square root of 1991797 is about 1411.3103840049. The cubic root of 1991797 is about 125.8196167477.

The spelling of 1991797 in words is "one million, nine hundred ninety-one thousand, seven hundred ninety-seven".