21759840 has 240 divisors, whose sum is σ = 81230688. Its totient is φ = 5474304.

The previous prime is 21759833. The next prime is 21759851. The reversal of 21759840 is 4895712.

21759840 is a `hidden beast` number, since 21 + 7 + 598 + 40 = 666.

It is a tau number, because it is divible by the number of its divisors (240).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a zygodrome in base 3.

It is a junction number, because it is equal to n+sod(n) for n = 21759795 and 21759804.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 298044 + ... + 298116.

Almost surely, 2^21759840 is an apocalyptic number.

21759840 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 21759840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40615344).

21759840 is an abundant number, since it is smaller than the sum of its proper divisors (59470848).

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

21759840 is a wasteful number, since it uses less digits than its factorization.

21759840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123 (or 106 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 36.

The square root of 21759840 is about 4664.7443659862. The cubic root of 21759840 is about 279.1805976068.

The spelling of 21759840 in words is "twenty-one million, seven hundred fifty-nine thousand, eight hundred forty".