21212221101991 has 2 divisors, whose sum is σ = 21212221101992. Its totient is φ = 21212221101990.

The previous prime is 21212221101959. The next prime is 21212221102021. The reversal of 21212221101991 is 19910112221212.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21212221101991 - 2⁵ = 21212221101959 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21212221101091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606110550995 + 10606110550996.

It is an arithmetic number, because the mean of its divisors is an integer number (10606110550996).

Almost surely, 2^{21212221101991} is an apocalyptic number.

21212221101991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212221101991 is an equidigital number, since it uses as much as digits as its factorization.

21212221101991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2592, while the sum is 34.

The spelling of 21212221101991 in words is "twenty-one trillion, two hundred twelve billion, two hundred twenty-one million, one hundred one thousand, nine hundred ninety-one".