21864517920 has 672 divisors, whose sum is σ = 90166728960. Its totient is φ = 4904478720.

The previous prime is 21864517901. The next prime is 21864517933. The reversal of 21864517920 is 2971546812.

It is a tau number, because it is divible by the number of its divisors (672).

It is a super-2 number, since 2×21864517920² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

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 111 ways as a sum of consecutive naturals, for example, 49805061 + ... + 49805499.

It is an arithmetic number, because the mean of its divisors is an integer number (134176680).

Almost surely, 2^21864517920 is an apocalyptic number.

21864517920 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 21864517920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (45083364480).

21864517920 is an abundant number, since it is smaller than the sum of its proper divisors (68302211040).

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

21864517920 is an equidigital number, since it uses as much as digits as its factorization.

21864517920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 540 (or 517 counting only the distinct ones).

The product of its (nonzero) digits is 241920, while the sum is 45.

The spelling of 21864517920 in words is "twenty-one billion, eight hundred sixty-four million, five hundred seventeen thousand, nine hundred twenty".