21987664 has 40 divisors (see below), whose sum is σ = 45432360. Its totient is φ = 10272768.

The previous prime is 21987631. The next prime is 21987671. The reversal of 21987664 is 46678912.

It can be written as a sum of positive squares in 4 ways, for example, as 10291264 + 11696400 = 3208^2 + 3420^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21987664.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 62112 + ... + 62464.

It is an arithmetic number, because the mean of its divisors is an integer number (1135809).

Almost surely, 2^21987664 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 21987664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22716180).

21987664 is an abundant number, since it is smaller than the sum of its proper divisors (23444696).

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

21987664 is a wasteful number, since it uses less digits than its factorization.

21987664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 607 (or 601 counting only the distinct ones).

The product of its digits is 145152, while the sum is 43.

The square root of 21987664 is about 4689.1005534111. The cubic root of 21987664 is about 280.1515506112.

The spelling of 21987664 in words is "twenty-one million, nine hundred eighty-seven thousand, six hundred sixty-four".