21605616 has 60 divisors (see below), whose sum is σ = 62716472. Its totient is φ = 7200576.

The previous prime is 21605611. The next prime is 21605627. The reversal of 21605616 is 61650612.

It is a happy number.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a self number, because there is not a number n which added to its sum of digits gives 21605616.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605611) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1110 + ... + 6666.

Almost surely, 2^21605616 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 21605616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31358236).

21605616 is an abundant number, since it is smaller than the sum of its proper divisors (41110856).

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

21605616 is an equidigital number, since it uses as much as digits as its factorization.

21605616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5580 (or 5562 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21605616 is about 4648.1841615840. The cubic root of 21605616 is about 278.5194641872.

It can be divided in two parts, 2160 and 5616, that added together give a 5-th power (7776 = 6⁵).

The spelling of 21605616 in words is "twenty-one million, six hundred five thousand, six hundred sixteen".