21978432 has 224 divisors, whose sum is σ = 78028800. Its totient is φ = 5930496.

The previous prime is 21978403. The next prime is 21978487. The reversal of 21978432 is 23487912.

21978432 is a `hidden beast` number, since 219 + 7 + 8 + 432 = 666.

It is a tau number, because it is divible by the number of its divisors (224).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 278169 + ... + 278247.

Almost surely, 2^21978432 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 21978432, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39014400).

21978432 is an abundant number, since it is smaller than the sum of its proper divisors (56050368).

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

21978432 is a wasteful number, since it uses less digits than its factorization.

21978432 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 130 (or 114 counting only the distinct ones).

The product of its digits is 24192, while the sum is 36.

The square root of 21978432 is about 4688.1160395195. The cubic root of 21978432 is about 280.1123358772.

The spelling of 21978432 in words is "twenty-one million, nine hundred seventy-eight thousand, four hundred thirty-two".