1991993 has 2 divisors, whose sum is σ = 1991994. Its totient is φ = 1991992.

The previous prime is 1991989. The next prime is 1991999. The reversal of 1991993 is 3991991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1841449 + 150544 = 1357^2 + 388^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991993 - 2² = 1991989 is a prime.

It is a super-2 number, since 2×1991993² = 7936072224098, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 1991993.

It is not a weakly prime, because it can be changed into another prime (1991999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995996 + 995997.

It is an arithmetic number, because the mean of its divisors is an integer number (995997).

2^1991993 is an apocalyptic number.

It is an amenable number.

1991993 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991993 is an equidigital number, since it uses as much as digits as its factorization.

1991993 is an evil number, because the sum of its binary digits is even.

The product of its digits is 19683, while the sum is 41.

The square root of 1991993 is about 1411.3798213096. The cubic root of 1991993 is about 125.8237436469.

The spelling of 1991993 in words is "one million, nine hundred ninety-one thousand, nine hundred ninety-three".