21861216 has 72 divisors (see below), whose sum is σ = 66961440. Its totient is φ = 6725376.

The previous prime is 21861209. The next prime is 21861221. The reversal of 21861216 is 61216812.

It is a tau number, because it is divible by the number of its divisors (72).

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

It is a self number, because there is not a number n which added to its sum of digits gives 21861216.

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 11 ways as a sum of consecutive naturals, for example, 825 + ... + 6663.

It is an arithmetic number, because the mean of its divisors is an integer number (930020).

Almost surely, 2^21861216 is an apocalyptic number.

21861216 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 21861216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33480720).

21861216 is an abundant number, since it is smaller than the sum of its proper divisors (45100224).

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

21861216 is a wasteful number, since it uses less digits than its factorization.

21861216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5868 (or 5857 counting only the distinct ones).

The product of its digits is 1152, while the sum is 27.

The square root of 21861216 is about 4675.5979296770. The cubic root of 21861216 is about 279.6134802885.

The spelling of 21861216 in words is "twenty-one million, eight hundred sixty-one thousand, two hundred sixteen".