1001220991 has 2 divisors, whose sum is σ = 1001220992. Its totient is φ = 1001220990.

The previous prime is 1001220977. The next prime is 1001221021. The reversal of 1001220991 is 1990221001.

It is a weak prime.

It is an emirp because it is prime and its reverse (1990221001) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1001220991 - 2⁷ = 1001220863 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1001220391) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 500610495 + 500610496.

It is an arithmetic number, because the mean of its divisors is an integer number (500610496).

Almost surely, 2^1001220991 is an apocalyptic number.

1001220991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1001220991 is an equidigital number, since it uses as much as digits as its factorization.

1001220991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324, while the sum is 25.

The square root of 1001220991 is about 31642.0762751119. The cubic root of 1001220991 is about 1000.4068314657.

Adding to 1001220991 its reverse (1990221001), we get a palindrome (2991441992).

The spelling of 1001220991 in words is "one billion, one million, two hundred twenty thousand, nine hundred ninety-one".