21305805840 has 600 divisors, whose sum is σ = 84231405720. Its totient is φ = 4981616640.

The previous prime is 21305805823. The next prime is 21305805907. The reversal of 21305805840 is 4850850312.

It is a happy number.

21305805840 is a `hidden beast` number, since 2 + 1 + 30 + 580 + 5 + 8 + 40 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 69155856 + 21236649984 = 8316^2 + 145728^2 .

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

It is a junction number, because it is equal to n+sod(n) for n = 21305805795 and 21305805804.

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 119 ways as a sum of consecutive naturals, for example, 22737852 + ... + 22738788.

Almost surely, 2^21305805840 is an apocalyptic number.

21305805840 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 21305805840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42115702860).

21305805840 is an abundant number, since it is smaller than the sum of its proper divisors (62925599880).

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

21305805840 is a wasteful number, since it uses less digits than its factorization.

21305805840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1013 (or 987 counting only the distinct ones).

The product of its (nonzero) digits is 38400, while the sum is 36.

The spelling of 21305805840 in words is "twenty-one billion, three hundred five million, eight hundred five thousand, eight hundred forty".