21978160 has 40 divisors (see below), whose sum is σ = 52295760. Its totient is φ = 8585472.

The previous prime is 21978139. The next prime is 21978167. The reversal of 21978160 is 6187912.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (40).

It is not an unprimeable number, because it can be changed into a prime (21978167) 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, 246 + ... + 6634.

It is an arithmetic number, because the mean of its divisors is an integer number (1307394).

Almost surely, 2^21978160 is an apocalyptic number.

21978160 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 21978160, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26147880).

21978160 is an abundant number, since it is smaller than the sum of its proper divisors (30317600).

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

21978160 is a wasteful number, since it uses less digits than its factorization.

21978160 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6445 (or 6439 counting only the distinct ones).

The product of its (nonzero) digits is 6048, while the sum is 34.

The square root of 21978160 is about 4688.0870299089. The cubic root of 21978160 is about 280.1111803373. Note that the first 4 decimals are identical.

The spelling of 21978160 in words is "twenty-one million, nine hundred seventy-eight thousand, one hundred sixty".