21195991871 has 4 divisors (see below), whose sum is σ = 21338247000. Its totient is φ = 21053736744.

The previous prime is 21195991793. The next prime is 21195991889. The reversal of 21195991871 is 17819959112.

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 21195991871 - 2¹⁴ = 21195975487 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 (21195991891) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 71127341 + ... + 71127638.

It is an arithmetic number, because the mean of its divisors is an integer number (5334561750).

Almost surely, 2^21195991871 is an apocalyptic number.

21195991871 is a deficient number, since it is larger than the sum of its proper divisors (142255129).

21195991871 is a wasteful number, since it uses less digits than its factorization.

21195991871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 142255128.

The product of its digits is 408240, while the sum is 53.

The spelling of 21195991871 in words is "twenty-one billion, one hundred ninety-five million, nine hundred ninety-one thousand, eight hundred seventy-one".