21987684 has 36 divisors (see below), whose sum is σ = 57499260. Its totient is φ = 7076160.

The previous prime is 21987671. The next prime is 21987689. The reversal of 21987684 is 48678912.

It can be written as a sum of positive squares in 2 ways, for example, as 18301284 + 3686400 = 4278^2 + 1920^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is a nialpdrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (21987689) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9487 + ... + 11574.

Almost surely, 2^21987684 is an apocalyptic number.

It is an amenable number.

21987684 is an abundant number, since it is smaller than the sum of its proper divisors (35511576).

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

21987684 is a wasteful number, since it uses less digits than its factorization.

21987684 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21100 (or 21095 counting only the distinct ones).

The product of its digits is 193536, while the sum is 45.

The square root of 21987684 is about 4689.1026860157. The cubic root of 21987684 is about 280.1516355532.

The spelling of 21987684 in words is "twenty-one million, nine hundred eighty-seven thousand, six hundred eighty-four".