21605016 has 64 divisors (see below), whose sum is σ = 56678400. Its totient is φ = 6854400.

The previous prime is 21605009. The next prime is 21605039. The reversal of 21605016 is 61050612.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21604983 and 21605001.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 52620 + ... + 53028.

It is an arithmetic number, because the mean of its divisors is an integer number (885600).

Almost surely, 2^21605016 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 21605016, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28339200).

21605016 is an abundant number, since it is smaller than the sum of its proper divisors (35073384).

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

21605016 is a wasteful number, since it uses less digits than its factorization.

21605016 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 520 (or 516 counting only the distinct ones).

The product of its (nonzero) digits is 360, while the sum is 21.

The square root of 21605016 is about 4648.1196198033. The cubic root of 21605016 is about 278.5168859497.

Adding to 21605016 its reverse (61050612), we get a palindrome (82655628).

The spelling of 21605016 in words is "twenty-one million, six hundred five thousand, sixteen".