21121357824 has 672 divisors, whose sum is σ = 75623708160. Its totient is φ = 5768921088.

The previous prime is 21121357819. The next prime is 21121357843. The reversal of 21121357824 is 42875312112.

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

It is a super-2 number, since 2×21121357824² (a number of 21 digits) contains 22 as substring.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 55 ways as a sum of consecutive naturals, for example, 449390569 + ... + 449390615.

It is an arithmetic number, because the mean of its divisors is an integer number (112535280).

Almost surely, 2^21121357824 is an apocalyptic number.

21121357824 is a gapful number since it is divisible by the number (24) 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 21121357824, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37811854080).

21121357824 is an abundant number, since it is smaller than the sum of its proper divisors (54502350336).

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

21121357824 is an frugal number, since it uses more digits than its factorization.

21121357824 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137 (or 102 counting only the distinct ones).

The product of its digits is 26880, while the sum is 36.

Adding to 21121357824 its reverse (42875312112), we get a palindrome (63996669936).

The spelling of 21121357824 in words is "twenty-one billion, one hundred twenty-one million, three hundred fifty-seven thousand, eight hundred twenty-four".