21609984 has 80 divisors (see below), whose sum is σ = 62853120. Its totient is φ = 6543360.

The previous prime is 21609977. The next prime is 21610003. The reversal of 21609984 is 48990612.

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, 16257 + ... + 17535.

It is an arithmetic number, because the mean of its divisors is an integer number (785664).

Almost surely, 2^21609984 is an apocalyptic number.

21609984 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 21609984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31426560).

21609984 is an abundant number, since it is smaller than the sum of its proper divisors (41243136).

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

21609984 is a wasteful number, since it uses less digits than its factorization.

21609984 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1311 (or 1295 counting only the distinct ones).

The product of its (nonzero) digits is 31104, while the sum is 39.

The square root of 21609984 is about 4648.6539987399. The cubic root of 21609984 is about 278.5382323174.

The spelling of 21609984 in words is "twenty-one million, six hundred nine thousand, nine hundred eighty-four".