21005568 has 90 divisors (see below), whose sum is σ = 62696634. Its totient is φ = 6994944.

The previous prime is 21005561. The next prime is 21005597. The reversal of 21005568 is 86550012.

21005568 is a `hidden beast` number, since 2 + 100 + 556 + 8 = 666.

It can be written as a sum of positive squares in only one way, i.e., 10969344 + 10036224 = 3312^2 + 3168^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 20230 + ... + 21242.

Almost surely, 2^21005568 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21005568, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31348317).

21005568 is an abundant number, since it is smaller than the sum of its proper divisors (41691066).

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

21005568 is an equidigital number, since it uses as much as digits as its factorization.

21005568 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1041 (or 1018 counting only the distinct ones).

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

The square root of 21005568 is about 4583.1831732978. The cubic root of 21005568 is about 275.9167991180.

The spelling of 21005568 in words is "twenty-one million, five thousand, five hundred sixty-eight".