21689984 has 32 divisors (see below), whose sum is σ = 44275140. Its totient is φ = 10577920.

The previous prime is 21689981. The next prime is 21690013. The reversal of 21689984 is 48998612.

It can be written as a sum of positive squares in 2 ways, for example, as 21160000 + 529984 = 4600^2 + 728^2 .

It is a tau number, because it is divible by the number of its divisors (32).

It is not an unprimeable number, because it can be changed into a prime (21689981) 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 3 ways as a sum of consecutive naturals, for example, 3182 + ... + 7314.

Almost surely, 2^21689984 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 21689984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22137570).

21689984 is an abundant number, since it is smaller than the sum of its proper divisors (22585156).

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

21689984 is an equidigital number, since it uses as much as digits as its factorization.

21689984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4188 (or 4176 counting only the distinct ones).

The product of its digits is 248832, while the sum is 47.

The square root of 21689984 is about 4657.2506911267. The cubic root of 21689984 is about 278.8815245315.

The spelling of 21689984 in words is "twenty-one million, six hundred eighty-nine thousand, nine hundred eighty-four".