It is an unprimeable number.
Almost surely, 221123344 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 21123344, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22458384).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
21123344 is a wasteful number, since it uses less digits than its factorization.
21123344 is an odious number, because the sum of its binary digits is odd.
The square root of 21123344 is about 4596.0139251312. The cubic root of 21123344 is about 276.4315171018.
Adding to 21123344 its reverse (44332112), we get a palindrome (65455456).
The spelling of 21123344 in words is "twenty-one million, one hundred twenty-three thousand, three hundred forty-four".