21855616 has 32 divisors (see below), whose sum is σ = 44155800. Its totient is φ = 10773504.

The previous prime is 21855607. The next prime is 21855619. The reversal of 21855616 is 61655812.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (32).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21855619) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8175 + ... + 10513.

Almost surely, 2^21855616 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 21855616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22077900).

21855616 is an abundant number, since it is smaller than the sum of its proper divisors (22300184).

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

21855616 is an equidigital number, since it uses as much as digits as its factorization.

21855616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2426 (or 2414 counting only the distinct ones).

The product of its digits is 14400, while the sum is 34.

The square root of 21855616 is about 4674.9990374331. Note that the first 3 decimals coincide. The cubic root of 21855616 is about 279.5896028547.

The spelling of 21855616 in words is "twenty-one million, eight hundred fifty-five thousand, six hundred sixteen".