21202111991 has 2 divisors, whose sum is σ = 21202111992. Its totient is φ = 21202111990.

The previous prime is 21202111967. The next prime is 21202111993. The reversal of 21202111991 is 19911120212.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21202111991 is a prime.

Together with 21202111993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21202111993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10601055995 + 10601055996.

It is an arithmetic number, because the mean of its divisors is an integer number (10601055996).

Almost surely, 2^21202111991 is an apocalyptic number.

21202111991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21202111991 is an equidigital number, since it uses as much as digits as its factorization.

21202111991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 648, while the sum is 29.

The spelling of 21202111991 in words is "twenty-one billion, two hundred two million, one hundred eleven thousand, nine hundred ninety-one".