21999840 has 48 divisors (see below), whose sum is σ = 69301008. Its totient is φ = 5866496.

The previous prime is 21999839. The next prime is 21999851. The reversal of 21999840 is 4899912.

It is a tau number, because it is divible by the number of its divisors (48).

It is a junction number, because it is equal to n+sod(n) for n = 21999792 and 21999801.

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, 22437 + ... + 23396.

It is an arithmetic number, because the mean of its divisors is an integer number (1443771).

Almost surely, 2^21999840 is an apocalyptic number.

21999840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21999840 is an abundant number, since it is smaller than the sum of its proper divisors (47301168).

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

21999840 is a wasteful number, since it uses less digits than its factorization.

21999840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45851 (or 45843 counting only the distinct ones).

The product of its (nonzero) digits is 46656, while the sum is 42.

The square root of 21999840 is about 4690.3987037351. The cubic root of 21999840 is about 280.2032537816.

The spelling of 21999840 in words is "twenty-one million, nine hundred ninety-nine thousand, eight hundred forty".