1991101001 has 4 divisors (see below), whose sum is σ = 1991312004. Its totient is φ = 1990890000.

The previous prime is 1991100967. The next prime is 1991101003. The reversal of 1991101001 is 1001011991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1001011991 = 7 ⋅143001713.

It can be written as a sum of positive squares in 2 ways, for example, as 1050084025 + 941016976 = 32405^2 + 30676^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991101001 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991101003) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 90650 + ... + 110451.

It is an arithmetic number, because the mean of its divisors is an integer number (497828001).

Almost surely, 2^1991101001 is an apocalyptic number.

It is an amenable number.

1991101001 is a deficient number, since it is larger than the sum of its proper divisors (211003).

1991101001 is an equidigital number, since it uses as much as digits as its factorization.

1991101001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 211002.

The product of its (nonzero) digits is 81, while the sum is 23.

The square root of 1991101001 is about 44621.7547951669. The cubic root of 1991101001 is about 1258.0495987768.

Adding to 1991101001 its reverse (1001011991), we get a palindrome (2992112992).

The spelling of 1991101001 in words is "one billion, nine hundred ninety-one million, one hundred one thousand, one".