21305856 has 160 divisors (see below), whose sum is σ = 67370688. Its totient is φ = 5898240.

The previous prime is 21305839. The next prime is 21305857. The reversal of 21305856 is 65850312.

It is not an unprimeable number, because it can be changed into a prime (21305857) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 219600 + ... + 219696.

Almost surely, 2^21305856 is an apocalyptic number.

21305856 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 21305856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33685344).

21305856 is an abundant number, since it is smaller than the sum of its proper divisors (46064832).

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

21305856 is a wasteful number, since it uses less digits than its factorization.

21305856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 142 (or 126 counting only the distinct ones).

The product of its (nonzero) digits is 7200, while the sum is 30.

The square root of 21305856 is about 4615.8266865211. The cubic root of 21305856 is about 277.2253853387.

The spelling of 21305856 in words is "twenty-one million, three hundred five thousand, eight hundred fifty-six".