21643521984 has 336 divisors, whose sum is σ = 79026105600. Its totient is φ = 5513453568.

The previous prime is 21643521973. The next prime is 21643521989. The reversal of 21643521984 is 48912534612.

21643521984 is a `hidden beast` number, since 2 + 1 + 6 + 43 + 521 + 9 + 84 = 666.

It is a tau number, because it is divible by the number of its divisors (336).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21643521989) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1294027 + ... + 1310645.

Almost surely, 2^21643521984 is an apocalyptic number.

21643521984 is a gapful number since it is divisible by the number (24) 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 21643521984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39513052800).

21643521984 is an abundant number, since it is smaller than the sum of its proper divisors (57382583616).

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

21643521984 is a wasteful number, since it uses less digits than its factorization.

21643521984 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16680 (or 16667 counting only the distinct ones).

The product of its digits is 414720, while the sum is 45.

The spelling of 21643521984 in words is "twenty-one billion, six hundred forty-three million, five hundred twenty-one thousand, nine hundred eighty-four".