21444 has 12 divisors (see below), whose sum is σ = 50064. Its totient is φ = 7144.

The previous prime is 21433. The next prime is 21467. The reversal of 21444 is 44412.

Subtracting from 21444 its product of digits (128), we obtain a square (21316 = 146^{2}).

Adding to 21444 its reverse (44412), we get a palindrome (65856).

It can be divided in two parts, 21 and 444, that added together give a triangular number (465 = T_{30}).

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 an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 882 + ... + 905.

It is an arithmetic number, because the mean of its divisors is an integer number (4172).

2^{21444} is an apocalyptic number.

It is an amenable number.

21444 is an abundant number, since it is smaller than the sum of its proper divisors (28620).

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

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25032).

21444 is a wasteful number, since it uses less digits than its factorization.

21444 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1794 (or 1792 counting only the distinct ones).

The product of its digits is 128, while the sum is 15.

The square root of 21444 is about 146.4377000639. The cubic root of 21444 is about 27.7823257738.

The spelling of 21444 in words is "twenty-one thousand, four hundred forty-four", and thus it is an iban number.

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