21002101101991 has 2 divisors, whose sum is σ = 21002101101992. Its totient is φ = 21002101101990.

The previous prime is 21002101101967. The next prime is 21002101102019. The reversal of 21002101101991 is 19910110120012.

It is a happy number.

It is an a-pointer prime, because the next prime (21002101102019) can be obtained adding 21002101101991 to its sum of digits (28).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21002101101991 - 2¹⁵ = 21002101069223 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21002101101791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501050550995 + 10501050550996.

It is an arithmetic number, because the mean of its divisors is an integer number (10501050550996).

Almost surely, 2^{21002101101991} is an apocalyptic number.

21002101101991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21002101101991 is an equidigital number, since it uses as much as digits as its factorization.

21002101101991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 324, while the sum is 28.

The spelling of 21002101101991 in words is "twenty-one trillion, two billion, one hundred one million, one hundred one thousand, nine hundred ninety-one".