21978208 has 48 divisors (see below), whose sum is σ = 50319360. Its totient is φ = 9254016.

The previous prime is 21978181. The next prime is 21978217. The reversal of 21978208 is 80287912.

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, 12385 + ... + 14047.

It is an arithmetic number, because the mean of its divisors is an integer number (1048320).

Almost surely, 2^21978208 is an apocalyptic number.

21978208 is a gapful number since it is divisible by the number (28) 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 21978208, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25159680).

21978208 is an abundant number, since it is smaller than the sum of its proper divisors (28341152).

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

21978208 is a wasteful number, since it uses less digits than its factorization.

21978208 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1739 (or 1731 counting only the distinct ones).

The product of its (nonzero) digits is 16128, while the sum is 37.

The square root of 21978208 is about 4688.0921492650. The cubic root of 21978208 is about 280.1113842568. Note that the first 3 decimals are identical.

The spelling of 21978208 in words is "twenty-one million, nine hundred seventy-eight thousand, two hundred eight".