21540686724 has 120 divisors (see below), whose sum is σ = 56752015320. Its totient is φ = 7124350464.

The previous prime is 21540686693. The next prime is 21540686749. The reversal of 21540686724 is 42768604512.

21540686724 is a `hidden beast` number, since 2 + 1 + 540 + 6 + 86 + 7 + 24 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 1140277824 + 20400408900 = 33768^2 + 142830^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21540686724.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 34911664 + ... + 34912280.

It is an arithmetic number, because the mean of its divisors is an integer number (472933461).

Almost surely, 2^21540686724 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21540686724, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28376007660).

21540686724 is an abundant number, since it is smaller than the sum of its proper divisors (35211328596).

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

21540686724 is a wasteful number, since it uses less digits than its factorization.

21540686724 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1299 (or 1288 counting only the distinct ones).

The product of its (nonzero) digits is 645120, while the sum is 45.

The spelling of 21540686724 in words is "twenty-one billion, five hundred forty million, six hundred eighty-six thousand, seven hundred twenty-four".