21606816 has 192 divisors, whose sum is σ = 73543680. Its totient is φ = 5391360.

The previous prime is 21606787. The next prime is 21606817. The reversal of 21606816 is 61860612.

It is not an unprimeable number, because it can be changed into a prime (21606817) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 273465 + ... + 273543.

It is an arithmetic number, because the mean of its divisors is an integer number (383040).

Almost surely, 2^21606816 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 21606816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36771840).

21606816 is an abundant number, since it is smaller than the sum of its proper divisors (51936864).

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

21606816 is a wasteful number, since it uses less digits than its factorization.

21606816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 147 (or 139 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 30.

The square root of 21606816 is about 4648.3132424569. The cubic root of 21606816 is about 278.5246205189.

It can be divided in two parts, 21606 and 816, that added together give a palindrome (22422).

The spelling of 21606816 in words is "twenty-one million, six hundred six thousand, eight hundred sixteen".