21005608 has 48 divisors (see below), whose sum is σ = 45325980. Its totient is φ = 9040896.

The previous prime is 21005597. The next prime is 21005609. The reversal of 21005608 is 80650012.

It is a happy number.

It can be written as a sum of positive squares in 6 ways, for example, as 13704804 + 7300804 = 3702^2 + 2702^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005609) 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 11 ways as a sum of consecutive naturals, for example, 192658 + ... + 192766.

Almost surely, 2^21005608 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 21005608, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22662990).

21005608 is an abundant number, since it is smaller than the sum of its proper divisors (24320372).

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

21005608 is a wasteful number, since it uses less digits than its factorization.

21005608 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 254 (or 141 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 22.

The square root of 21005608 is about 4583.1875370750. The cubic root of 21005608 is about 275.9169742567.

The spelling of 21005608 in words is "twenty-one million, five thousand, six hundred eight".