21021212311991 has 2 divisors, whose sum is σ = 21021212311992. Its totient is φ = 21021212311990.

The previous prime is 21021212311963. The next prime is 21021212311993. The reversal of 21021212311991 is 19911321212012.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21021212311991 - 2¹⁸ = 21021212049847 is a prime.

Together with 21021212311993, 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 (21021212311993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510606155995 + 10510606155996.

It is an arithmetic number, because the mean of its divisors is an integer number (10510606155996).

Almost surely, 2^{21021212311991} is an apocalyptic number.

21021212311991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21021212311991 is an equidigital number, since it uses as much as digits as its factorization.

21021212311991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3888, while the sum is 35.

The spelling of 21021212311991 in words is "twenty-one trillion, twenty-one billion, two hundred twelve million, three hundred eleven thousand, nine hundred ninety-one".