It is a happy number.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12211222 = 2 ⋅6105611.
It is a cyclic number.
It is a Duffinian number.
It is a congruent number.
Almost surely, 222211221 is an apocalyptic number.
It is an amenable number.
22211221 is an equidigital number, since it uses as much as digits as its factorization.
22211221 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 716522.
The square root of 22211221 is about 4712.8782076349. The cubic root of 22211221 is about 281.0978201584.
Adding to 22211221 its reverse (12211222), we get a palindrome (34422443).
Subtracting from 22211221 its reverse (12211222), we obtain a palindrome (9999999).
The spelling of 22211221 in words is "twenty-two million, two hundred eleven thousand, two hundred twenty-one".