21993840 has 120 divisors (see below), whose sum is σ = 80606448. Its totient is φ = 5329920.

The previous prime is 21993833. The next prime is 21993857. The reversal of 21993840 is 4839912.

It is a tau number, because it is divible by the number of its divisors (120).

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

It is a junction number, because it is equal to n+sod(n) for n = 21993795 and 21993804.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6532 + ... + 9308.

Almost surely, 2^21993840 is an apocalyptic number.

21993840 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 21993840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40303224).

21993840 is an abundant number, since it is smaller than the sum of its proper divisors (58612608).

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

21993840 is a wasteful number, since it uses less digits than its factorization.

21993840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2807 (or 2798 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 36.

The square root of 21993840 is about 4689.7590556445. The cubic root of 21993840 is about 280.1777782572.

The spelling of 21993840 in words is "twenty-one million, nine hundred ninety-three thousand, eight hundred forty".