21001200009991 has 2 divisors, whose sum is σ = 21001200009992. Its totient is φ = 21001200009990.

The previous prime is 21001200009989. The next prime is 21001200010001. The reversal of 21001200009991 is 19990000210012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21001200009991 - 2¹ = 21001200009989 is a prime.

It is a super-3 number, since 3×21001200009991³ (a number of 41 digits) contains 333 as substring.

Together with 21001200009989, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21001200039991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500600004995 + 10500600004996.

It is an arithmetic number, because the mean of its divisors is an integer number (10500600004996).

Almost surely, 2^{21001200009991} is an apocalyptic number.

21001200009991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001200009991 is an equidigital number, since it uses as much as digits as its factorization.

21001200009991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2916, while the sum is 34.

The spelling of 21001200009991 in words is "twenty-one trillion, one billion, two hundred million, nine thousand, nine hundred ninety-one".