21801972191 has 4 divisors (see below), whose sum is σ = 21994910112. Its totient is φ = 21609034272.

The previous prime is 21801972163. The next prime is 21801972217. The reversal of 21801972191 is 19127910812.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21801972191 - 2¹⁰ = 21801971167 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21801972991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 96468791 + ... + 96469016.

It is an arithmetic number, because the mean of its divisors is an integer number (5498727528).

Almost surely, 2^21801972191 is an apocalyptic number.

21801972191 is a deficient number, since it is larger than the sum of its proper divisors (192937921).

21801972191 is a wasteful number, since it uses less digits than its factorization.

21801972191 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 192937920.

The product of its (nonzero) digits is 18144, while the sum is 41.

The spelling of 21801972191 in words is "twenty-one billion, eight hundred one million, nine hundred seventy-two thousand, one hundred ninety-one".