21017984 has 64 divisors (see below), whose sum is σ = 47809440. Its totient is φ = 9117696.

The previous prime is 21017981. The next prime is 21017993. The reversal of 21017984 is 48971012.

It is a tau number, because it is divible by the number of its divisors (64).

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a self number, because there is not a number n which added to its sum of digits gives 21017984.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21017981) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 27917 + ... + 28659.

Almost surely, 2^21017984 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 21017984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23904720).

21017984 is an abundant number, since it is smaller than the sum of its proper divisors (26791456).

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

21017984 is a wasteful number, since it uses less digits than its factorization.

21017984 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 787 (or 775 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 32.

The square root of 21017984 is about 4584.5374903037. The cubic root of 21017984 is about 275.9711515041.

Adding to 21017984 its reverse (48971012), we get a palindrome (69988996).

The spelling of 21017984 in words is "twenty-one million, seventeen thousand, nine hundred eighty-four".