20100991 has 2 divisors, whose sum is σ = 20100992. Its totient is φ = 20100990.

The previous prime is 20100943. The next prime is 20101001. The reversal of 20100991 is 19900102.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20100991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20100911) 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 as a sum of consecutive naturals, namely, 10050495 + 10050496.

It is an arithmetic number, because the mean of its divisors is an integer number (10050496).

Almost surely, 2^20100991 is an apocalyptic number.

20100991 is a deficient number, since it is larger than the sum of its proper divisors (1).

20100991 is an equidigital number, since it uses as much as digits as its factorization.

20100991 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 22.

The square root of 20100991 is about 4483.4128741395. The cubic root of 20100991 is about 271.8978810355.

The spelling of 20100991 in words is "twenty million, one hundred thousand, nine hundred ninety-one".