21243856824 has 128 divisors (see below), whose sum is σ = 61000243200. Its totient is φ = 6843191040.

The previous prime is 21243856819. The next prime is 21243856831. The reversal of 21243856824 is 42865834212.

21243856824 is a `hidden beast` number, since 21 + 2 + 43 + 8 + 568 + 24 = 666.

It is a super-2 number, since 2×21243856824² (a number of 21 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21243856824.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5910772 + ... + 5914364.

It is an arithmetic number, because the mean of its divisors is an integer number (476564400).

Almost surely, 2^21243856824 is an apocalyptic number.

21243856824 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 21243856824, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30500121600).

21243856824 is an abundant number, since it is smaller than the sum of its proper divisors (39756386376).

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

21243856824 is a wasteful number, since it uses less digits than its factorization.

21243856824 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4522 (or 4512 counting only the distinct ones).

The product of its digits is 737280, while the sum is 45.

The spelling of 21243856824 in words is "twenty-one billion, two hundred forty-three million, eight hundred fifty-six thousand, eight hundred twenty-four".