21111210111991 has 2 divisors, whose sum is σ = 21111210111992. Its totient is φ = 21111210111990.

The previous prime is 21111210111967. The next prime is 21111210112049. The reversal of 21111210111991 is 19911101211112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21111210111991 - 2¹⁷ = 21111209980919 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21111210111941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10555605055995 + 10555605055996.

It is an arithmetic number, because the mean of its divisors is an integer number (10555605055996).

Almost surely, 2^{21111210111991} is an apocalyptic number.

21111210111991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21111210111991 is an equidigital number, since it uses as much as digits as its factorization.

21111210111991 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 31.

The spelling of 21111210111991 in words is "twenty-one trillion, one hundred eleven billion, two hundred ten million, one hundred eleven thousand, nine hundred ninety-one".