21684512768 has 48 divisors (see below), whose sum is σ = 43507622340. Its totient is φ = 10804953088.

The previous prime is 21684512767. The next prime is 21684512789. The reversal of 21684512768 is 86721548612.

It can be written as a sum of positive squares in 2 ways, for example, as 19474760704 + 2209752064 = 139552^2 + 47008^2 .

It is not an unprimeable number, because it can be changed into a prime (21684512761) 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, 581996 + ... + 618132.

Almost surely, 2^21684512768 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 21684512768, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21753811170).

21684512768 is an abundant number, since it is smaller than the sum of its proper divisors (21823109572).

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

21684512768 is an equidigital number, since it uses as much as digits as its factorization.

21684512768 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36452 (or 36432 counting only the distinct ones).

The product of its digits is 1290240, while the sum is 50.

The spelling of 21684512768 in words is "twenty-one billion, six hundred eighty-four million, five hundred twelve thousand, seven hundred sixty-eight".