20121221209 has 4 divisors (see below), whose sum is σ = 20171399220.
Its totient is φ = 20071043200.
The previous prime is 20121221161. The next prime is 20121221249. The reversal of 20121221209 is 90212212102.
It is a semiprime because it is the product of two primes.
It can be written as a sum of positive squares in 2 ways, for example, as 13410334809 + 6710886400 = 115803^2 + 81920^2
It is a cyclic number.
It is not a de Polignac number, because 20121221209 - 217 = 20121090137 is a prime.
It is a super-3 number, since 3×201212212093 (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.
It is a Duffinian number.
It is a self number, because there is not a number n which added to its sum of digits gives 20121221209.
It is not an unprimeable number, because it can be changed into a prime (20121221249) 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, 25088404 + ... + 25089205.
It is an arithmetic number, because the mean of its divisors is an integer number (5042849805).
Almost surely, 220121221209 is an apocalyptic number.
It is an amenable number.
20121221209 is a deficient number, since it is larger than the sum of its proper divisors (50178011).
20121221209 is an equidigital number, since it uses as much as digits as its factorization.
20121221209 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 50178010.
The product of its (nonzero) digits is 288, while the sum is 22.
It can be divided in two parts, 2012 and 1221209, that added together give a palindrome (1223221).
The spelling of 20121221209 in words is "twenty billion, one hundred twenty-one million, two hundred twenty-one thousand, two hundred nine".