21987984 has 40 divisors (see below), whose sum is σ = 57451680. Its totient is φ = 7245568.

The previous prime is 21987967. The next prime is 21987989. The reversal of 21987984 is 48978912.

It is a Harshad number since it is a multiple of its sum of digits (48).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987989) 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, 1699 + ... + 6845.

It is an arithmetic number, because the mean of its divisors is an integer number (1436292).

Almost surely, 2^21987984 is an apocalyptic number.

21987984 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 21987984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28725840).

21987984 is an abundant number, since it is smaller than the sum of its proper divisors (35463696).

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

21987984 is a wasteful number, since it uses less digits than its factorization.

21987984 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5247 (or 5241 counting only the distinct ones).

The product of its digits is 290304, while the sum is 48.

The square root of 21987984 is about 4689.1346749694. The cubic root of 21987984 is about 280.1529096772.

The spelling of 21987984 in words is "twenty-one million, nine hundred eighty-seven thousand, nine hundred eighty-four".