21216444 has 12 divisors (see below), whose sum is σ = 49505064. Its totient is φ = 7072144.

The previous prime is 21216427. The next prime is 21216451. The reversal of 21216444 is 44461212.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (12).

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 884007 + ... + 884030.

It is an arithmetic number, because the mean of its divisors is an integer number (4125422).

Almost surely, 2^21216444 is an apocalyptic number.

It is an amenable number.

21216444 is an abundant number, since it is smaller than the sum of its proper divisors (28288620).

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

21216444 is a wasteful number, since it uses less digits than its factorization.

21216444 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1768044 (or 1768042 counting only the distinct ones).

The product of its digits is 1536, while the sum is 24.

The square root of 21216444 is about 4606.1311314377. The cubic root of 21216444 is about 276.8370409127.

Adding to 21216444 its reverse (44461212), we get a palindrome (65677656).

The spelling of 21216444 in words is "twenty-one million, two hundred sixteen thousand, four hundred forty-four".