21011199991 has 2 divisors, whose sum is σ = 21011199992. Its totient is φ = 21011199990.

The previous prime is 21011199971. The next prime is 21011200043. The reversal of 21011199991 is 19999111012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21011199991 - 2⁹ = 21011199479 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21011199971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505599995 + 10505599996.

It is an arithmetic number, because the mean of its divisors is an integer number (10505599996).

Almost surely, 2^21011199991 is an apocalyptic number.

21011199991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21011199991 is an equidigital number, since it uses as much as digits as its factorization.

21011199991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 13122, while the sum is 43.

The spelling of 21011199991 in words is "twenty-one billion, eleven million, one hundred ninety-nine thousand, nine hundred ninety-one".