21605688 has 96 divisors (see below), whose sum is σ = 64668240. Its totient is φ = 6474240.

The previous prime is 21605677. The next prime is 21605693. The reversal of 21605688 is 88650612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 38095 + ... + 38657.

Almost surely, 2^21605688 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 21605688, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32334120).

21605688 is an abundant number, since it is smaller than the sum of its proper divisors (43062552).

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

21605688 is a wasteful number, since it uses less digits than its factorization.

21605688 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 629 (or 622 counting only the distinct ones).

The product of its (nonzero) digits is 23040, while the sum is 36.

The square root of 21605688 is about 4648.1919065374. The cubic root of 21605688 is about 278.5197735725.

The spelling of 21605688 in words is "twenty-one million, six hundred five thousand, six hundred eighty-eight".