It is a weak prime.
It is a cyclic number.
Almost surely, 2221421255544681 is an apocalyptic number.
It is an amenable number.
221421255544681 is an equidigital number, since it uses as much as digits as its factorization.
221421255544681 is an odious number, because the sum of its binary digits is odd.
The spelling of 221421255544681 in words is "two hundred twenty-one trillion, four hundred twenty-one billion, two hundred fifty-five million, five hundred forty-four thousand, six hundred eighty-one".