It is a congruent number.
It is an unprimeable number.
Almost surely, 221224521656256 is an apocalyptic number.
It is an amenable number.
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
21224521656256 is an equidigital number, since it uses as much as digits as its factorization.
21224521656256 is an odious number, because the sum of its binary digits is odd.
The spelling of 21224521656256 in words is "twenty-one trillion, two hundred twenty-four billion, five hundred twenty-one million, six hundred fifty-six thousand, two hundred fifty-six".