21805056 has 216 divisors, whose sum is σ = 77936040. Its totient is φ = 5750784.

The previous prime is 21805037. The next prime is 21805073. The reversal of 21805056 is 65050812.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 1677306 + ... + 1677318.

It is an arithmetic number, because the mean of its divisors is an integer number (360815).

Almost surely, 2^21805056 is an apocalyptic number.

21805056 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 21805056, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38968020).

21805056 is an abundant number, since it is smaller than the sum of its proper divisors (56130984).

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

21805056 is a wasteful number, since it uses less digits than its factorization.

21805056 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61 (or 25 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 27.

The square root of 21805056 is about 4669.5884186939. The cubic root of 21805056 is about 279.3738388613.

Adding to 21805056 its reverse (65050812), we get a palindrome (86855868).

The spelling of 21805056 in words is "twenty-one million, eight hundred five thousand, fifty-six".