21402665856 has 768 divisors, whose sum is σ = 77792870400. Its totient is φ = 5748019200.

The previous prime is 21402665849. The next prime is 21402665903. The reversal of 21402665856 is 65856620412.

21402665856 is a `hidden beast` number, since 2 + 1 + 4 + 0 + 2 + 66 + 585 + 6 = 666.

It is a Smith number, since the sum of its digits (45) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 168524865 + ... + 168524991.

It is an arithmetic number, because the mean of its divisors is an integer number (101292800).

Almost surely, 2^21402665856 is an apocalyptic number.

21402665856 is a gapful number since it is divisible by the number (26) 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 21402665856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38896435200).

21402665856 is an abundant number, since it is smaller than the sum of its proper divisors (56390204544).

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

21402665856 is a wasteful number, since it uses less digits than its factorization.

21402665856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 216 (or 187 counting only the distinct ones).

The product of its (nonzero) digits is 691200, while the sum is 45.

The spelling of 21402665856 in words is "twenty-one billion, four hundred two million, six hundred sixty-five thousand, eight hundred fifty-six".