21609808 has 40 divisors (see below), whose sum is σ = 45979200. Its totient is φ = 9757440.

The previous prime is 21609787. The next prime is 21609817. The reversal of 21609808 is 80890612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 34716 + ... + 35332.

It is an arithmetic number, because the mean of its divisors is an integer number (1149480).

Almost surely, 2^21609808 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 21609808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22989600).

21609808 is an abundant number, since it is smaller than the sum of its proper divisors (24369392).

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

21609808 is a wasteful number, since it uses less digits than its factorization.

21609808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 835 (or 829 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 34.

The square root of 21609808 is about 4648.6350684905. The cubic root of 21609808 is about 278.5374761413.

The spelling of 21609808 in words is "twenty-one million, six hundred nine thousand, eight hundred eight".