21666827520 has 648 divisors, whose sum is σ = 84027041280. Its totient is φ = 5146951680.

The previous prime is 21666827519. The next prime is 21666827579. The reversal of 21666827520 is 2572866612.

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

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 71 ways as a sum of consecutive naturals, for example, 60353101 + ... + 60353459.

It is an arithmetic number, because the mean of its divisors is an integer number (129671360).

Almost surely, 2^21666827520 is an apocalyptic number.

21666827520 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 21666827520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42013520640).

21666827520 is an abundant number, since it is smaller than the sum of its proper divisors (62360213760).

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

21666827520 is a wasteful number, since it uses less digits than its factorization.

21666827520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 443 (or 413 counting only the distinct ones).

The product of its (nonzero) digits is 483840, while the sum is 45.

The spelling of 21666827520 in words is "twenty-one billion, six hundred sixty-six million, eight hundred twenty-seven thousand, five hundred twenty".