1001121991 has 2 divisors, whose sum is σ = 1001121992. Its totient is φ = 1001121990.

The previous prime is 1001121977. The next prime is 1001122009. The reversal of 1001121991 is 1991211001.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1001121991 - 2¹⁷ = 1000990919 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1001121931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 500560995 + 500560996.

It is an arithmetic number, because the mean of its divisors is an integer number (500560996).

Almost surely, 2^1001121991 is an apocalyptic number.

1001121991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1001121991 is an equidigital number, since it uses as much as digits as its factorization.

1001121991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 162, while the sum is 25.

The square root of 1001121991 is about 31640.5118637483. The cubic root of 1001121991 is about 1000.3738572134.

Adding to 1001121991 its reverse (1991211001), we get a palindrome (2992332992).

The spelling of 1001121991 in words is "one billion, one million, one hundred twenty-one thousand, nine hundred ninety-one".