21642216 has 64 divisors (see below), whose sum is σ = 58828800. Its totient is φ = 6609600.

The previous prime is 21642199. The next prime is 21642217. The reversal of 21642216 is 61224612.

It is a Harshad number since it is a multiple of its sum of digits (24).

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

It is not an unprimeable number, because it can be changed into a prime (21642217) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13371 + ... + 14901.

It is an arithmetic number, because the mean of its divisors is an integer number (919200).

Almost surely, 2^21642216 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 21642216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29414400).

21642216 is an abundant number, since it is smaller than the sum of its proper divisors (37186584).

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

21642216 is a wasteful number, since it uses less digits than its factorization.

21642216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1590 (or 1586 counting only the distinct ones).

The product of its digits is 1152, while the sum is 24.

The square root of 21642216 is about 4652.1195169514. The cubic root of 21642216 is about 278.6766464939.

Adding to 21642216 its reverse (61224612), we get a palindrome (82866828).

The spelling of 21642216 in words is "twenty-one million, six hundred forty-two thousand, two hundred sixteen".