21212109999991 has 2 divisors, whose sum is σ = 21212109999992. Its totient is φ = 21212109999990.

The previous prime is 21212109999947. The next prime is 21212110000021. The reversal of 21212109999991 is 19999990121212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21212109999991 - 2¹⁹ = 21212109475703 is a prime.

It is a super-3 number, since 3×21212109999991³ (a number of 41 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21212109999911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606054999995 + 10606054999996.

It is an arithmetic number, because the mean of its divisors is an integer number (10606054999996).

Almost surely, 2^{21212109999991} is an apocalyptic number.

21212109999991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212109999991 is an equidigital number, since it uses as much as digits as its factorization.

21212109999991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4251528, while the sum is 64.

The spelling of 21212109999991 in words is "twenty-one trillion, two hundred twelve billion, one hundred nine million, nine hundred ninety-nine thousand, nine hundred ninety-one".