It is a nude number because it is divisible by every one of its digits.
It is a congruent number.
It is an unprimeable number.
Almost surely, 221222212121212 is an apocalyptic number.
It is an amenable number.
21222212121212 is a wasteful number, since it uses less digits than its factorization.
21222212121212 is an odious number, because the sum of its binary digits is odd.
Adding to 21222212121212 its reverse (21212121222212), we get a palindrome (42434333343424).
The spelling of 21222212121212 in words is "twenty-one trillion, two hundred twenty-two billion, two hundred twelve million, one hundred twenty-one thousand, two hundred twelve".