209121221 has 4 divisors (see below), whose sum is σ = 218213472. Its totient is φ = 200028972.

The previous prime is 209121217. The next prime is 209121223. The reversal of 209121221 is 122121902.

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.

It is a cyclic number.

It is not a de Polignac number, because 209121221 - 2² = 209121217 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 209121193 and 209121202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (209121223) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4546091 + ... + 4546136.

It is an arithmetic number, because the mean of its divisors is an integer number (54553368).

Almost surely, 2^209121221 is an apocalyptic number.

It is an amenable number.

209121221 is a deficient number, since it is larger than the sum of its proper divisors (9092251).

209121221 is an equidigital number, since it uses as much as digits as its factorization.

209121221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9092250.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 209121221 is about 14461.0242030086. The cubic root of 209121221 is about 593.5619259396.

It can be divided in two parts, 20912 and 1221, that multiplied together give a palindrome (25533552).

The spelling of 209121221 in words is "two hundred nine million, one hundred twenty-one thousand, two hundred twenty-one".