21921840 has 200 divisors, whose sum is σ = 81021600. Its totient is φ = 5474304.

The previous prime is 21921817. The next prime is 21921847. The reversal of 21921840 is 4812912.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21921847) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 110061 + ... + 110259.

It is an arithmetic number, because the mean of its divisors is an integer number (405108).

Almost surely, 2^21921840 is an apocalyptic number.

21921840 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 21921840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40510800).

21921840 is an abundant number, since it is smaller than the sum of its proper divisors (59099760).

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

21921840 is a wasteful number, since it uses less digits than its factorization.

21921840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 241 (or 226 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 27.

The square root of 21921840 is about 4682.0764624256. The cubic root of 21921840 is about 279.8717099367.

The spelling of 21921840 in words is "twenty-one million, nine hundred twenty-one thousand, eight hundred forty".