1215212221 has 4 divisors (see below), whose sum is σ = 1215757692. Its totient is φ = 1214666752.

The previous prime is 1215212189. The next prime is 1215212261. The reversal of 1215212221 is 1222125121.

It is a happy number.

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 1143386596 + 71825625 = 33814^2 + 8475^2 .

It is a cyclic number.

It is not a de Polignac number, because 1215212221 - 2⁵ = 1215212189 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1215212261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 269380 + ... + 273853.

It is an arithmetic number, because the mean of its divisors is an integer number (303939423).

Almost surely, 2^1215212221 is an apocalyptic number.

It is an amenable number.

1215212221 is a deficient number, since it is larger than the sum of its proper divisors (545471).

1215212221 is an equidigital number, since it uses as much as digits as its factorization.

1215212221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 545470.

The product of its digits is 160, while the sum is 19.

The square root of 1215212221 is about 34859.8941622031. The cubic root of 1215212221 is about 1067.1301150926.

Adding to 1215212221 its reverse (1222125121), we get a palindrome (2437337342).

The spelling of 1215212221 in words is "one billion, two hundred fifteen million, two hundred twelve thousand, two hundred twenty-one".