21640843187 has 4 divisors (see below), whose sum is σ = 21642222096. Its totient is φ = 21639464280.

The previous prime is 21640843171. The next prime is 21640843199. The reversal of 21640843187 is 78134804612.

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 21640843187 - 2⁴ = 21640843171 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21640843127) 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, 665639 + ... + 697392.

It is an arithmetic number, because the mean of its divisors is an integer number (5410555524).

Almost surely, 2^21640843187 is an apocalyptic number.

21640843187 is a deficient number, since it is larger than the sum of its proper divisors (1378909).

21640843187 is a wasteful number, since it uses less digits than its factorization.

21640843187 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1378908.

The product of its (nonzero) digits is 258048, while the sum is 44.

The spelling of 21640843187 in words is "twenty-one billion, six hundred forty million, eight hundred forty-three thousand, one hundred eighty-seven".