21681256872 has 64 divisors (see below), whose sum is σ = 59275569600. Its totient is φ = 6553981440.

The previous prime is 21681256721. The next prime is 21681256879. The reversal of 21681256872 is 27865218612.

It is not an unprimeable number, because it can be changed into a prime (21681256879) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7578 + ... + 208374.

It is an arithmetic number, because the mean of its divisors is an integer number (926180775).

Almost surely, 2^21681256872 is an apocalyptic number.

21681256872 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21681256872, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29637784800).

21681256872 is an abundant number, since it is smaller than the sum of its proper divisors (37594312728).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21681256872 is a wasteful number, since it uses less digits than its factorization.

21681256872 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201226 (or 201222 counting only the distinct ones).

The product of its digits is 645120, while the sum is 48.

The spelling of 21681256872 in words is "twenty-one billion, six hundred eighty-one million, two hundred fifty-six thousand, eight hundred seventy-two".