21009984 has 56 divisors (see below), whose sum is σ = 56388000. Its totient is φ = 6902784.

The previous prime is 21009983. The next prime is 21009997. The reversal of 21009984 is 48990012.

It is a super-4 number, since 4×21009984⁴ (a number of 30 digits) contains 4444 as substring.

It is not an unprimeable number, because it can be changed into a prime (21009983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13267 + ... + 14765.

Almost surely, 2^21009984 is an apocalyptic number.

21009984 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 21009984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28194000).

21009984 is an abundant number, since it is smaller than the sum of its proper divisors (35378016).

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

21009984 is a wasteful number, since it uses less digits than its factorization.

21009984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1587 (or 1577 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 33.

The square root of 21009984 is about 4583.6649092184. The cubic root of 21009984 is about 275.9361330903.

Adding to 21009984 its reverse (48990012), we get a palindrome (69999996).

The spelling of 21009984 in words is "twenty-one million, nine thousand, nine hundred eighty-four".