21978740 has 48 divisors (see below), whose sum is σ = 54187392. Its totient is φ = 7330176.

The previous prime is 21978701. The next prime is 21978743. The reversal of 21978740 is 4787912.

It is a junction number, because it is equal to n+sod(n) for n = 21978694 and 21978703.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21978743) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3059 + ... + 7301.

It is an arithmetic number, because the mean of its divisors is an integer number (1128904).

Almost surely, 2^21978740 is an apocalyptic number.

21978740 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 21978740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27093696).

21978740 is an abundant number, since it is smaller than the sum of its proper divisors (32208652).

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

21978740 is a wasteful number, since it uses less digits than its factorization.

21978740 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4296 (or 4294 counting only the distinct ones).

The product of its (nonzero) digits is 28224, while the sum is 38.

The square root of 21978740 is about 4688.1488884207. The cubic root of 21978740 is about 280.1136443448.

The spelling of 21978740 in words is "twenty-one million, nine hundred seventy-eight thousand, seven hundred forty".