21178320 has 80 divisors (see below), whose sum is σ = 66543360. Its totient is φ = 5571072.

The previous prime is 21178309. The next prime is 21178321. The reversal of 21178320 is 2387112.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21178321) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18402 + ... + 19518.

It is an arithmetic number, because the mean of its divisors is an integer number (831792).

Almost surely, 2^21178320 is an apocalyptic number.

21178320 is a gapful number since it is divisible by the number (20) 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 21178320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33271680).

21178320 is an abundant number, since it is smaller than the sum of its proper divisors (45365040).

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

21178320 is a wasteful number, since it uses less digits than its factorization.

21178320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1212 (or 1206 counting only the distinct ones).

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21178320 is about 4601.9908735242. The cubic root of 21178320 is about 276.6711245874.

The spelling of 21178320 in words is "twenty-one million, one hundred seventy-eight thousand, three hundred twenty".