21681444 has 24 divisors (see below), whose sum is σ = 52335360. Its totient is φ = 6977824.

The previous prime is 21681421. The next prime is 21681449. The reversal of 21681444 is 44418612.

It is a hoax number, since the sum of its digits (30) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21681449) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 30804 + ... + 31499.

It is an arithmetic number, because the mean of its divisors is an integer number (2180640).

Almost surely, 2^21681444 is an apocalyptic number.

It is an amenable number.

21681444 is an abundant number, since it is smaller than the sum of its proper divisors (30653916).

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

21681444 is a wasteful number, since it uses less digits than its factorization.

21681444 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62339 (or 62337 counting only the distinct ones).

The product of its digits is 6144, while the sum is 30.

The square root of 21681444 is about 4656.3337509246. Note that the first 3 decimals coincide. The cubic root of 21681444 is about 278.8449183747.

The spelling of 21681444 in words is "twenty-one million, six hundred eighty-one thousand, four hundred forty-four".