21681382871 has 4 divisors (see below), whose sum is σ = 22956758352. Its totient is φ = 20406007392.

The previous prime is 21681382861. The next prime is 21681382903. The reversal of 21681382871 is 17828318612.

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

It is a de Polignac number, because none of the positive numbers 2^k-21681382871 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 (21681382831) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 637687715 + ... + 637687748.

It is an arithmetic number, because the mean of its divisors is an integer number (5739189588).

Almost surely, 2^21681382871 is an apocalyptic number.

21681382871 is a deficient number, since it is larger than the sum of its proper divisors (1275375481).

21681382871 is a wasteful number, since it uses less digits than its factorization.

21681382871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1275375480.

The product of its digits is 258048, while the sum is 47.

The spelling of 21681382871 in words is "twenty-one billion, six hundred eighty-one million, three hundred eighty-two thousand, eight hundred seventy-one".