21017808 has 120 divisors (see below), whose sum is σ = 69638400. Its totient is φ = 5789952.

The previous prime is 21017803. The next prime is 21017809. The reversal of 21017808 is 80871012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21017803) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 28873 + ... + 29591.

It is an arithmetic number, because the mean of its divisors is an integer number (580320).

Almost surely, 2^21017808 is an apocalyptic number.

21017808 is a gapful number since it is divisible by the number (28) 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 21017808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34819200).

21017808 is an abundant number, since it is smaller than the sum of its proper divisors (48620592).

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

21017808 is a wasteful number, since it uses less digits than its factorization.

21017808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 769 (or 760 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 27.

The square root of 21017808 is about 4584.5182953065. The cubic root of 21017808 is about 275.9703811946.

The spelling of 21017808 in words is "twenty-one million, seventeen thousand, eight hundred eight".