21221616 has 80 divisors (see below), whose sum is σ = 59996160. Its totient is φ = 6424320.

The previous prime is 21221597. The next prime is 21221621. The reversal of 21221616 is 61612212.

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 21221592 and 21221601.

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, 44065 + ... + 44543.

It is an arithmetic number, because the mean of its divisors is an integer number (749952).

Almost surely, 2^21221616 is an apocalyptic number.

21221616 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21221616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29998080).

21221616 is an abundant number, since it is smaller than the sum of its proper divisors (38774544).

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

21221616 is a wasteful number, since it uses less digits than its factorization.

21221616 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 574 (or 568 counting only the distinct ones).

The product of its digits is 288, while the sum is 21.

The square root of 21221616 is about 4606.6925228411. The cubic root of 21221616 is about 276.8595342335.

Adding to 21221616 its reverse (61612212), we get a palindrome (82833828).

The spelling of 21221616 in words is "twenty-one million, two hundred twenty-one thousand, six hundred sixteen".