1221815221 has 8 divisors (see below), whose sum is σ = 1368913824. Its totient is φ = 1080720720.

The previous prime is 1221815213. The next prime is 1221815233. The reversal of 1221815221 is 1225181221.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1221815221 - 2³ = 1221815213 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 (1221815261) 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 7 ways as a sum of consecutive naturals, for example, 1500595 + ... + 1501408.

It is an arithmetic number, because the mean of its divisors is an integer number (171114228).

Almost surely, 2^1221815221 is an apocalyptic number.

1221815221 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1221815221 is a deficient number, since it is larger than the sum of its proper divisors (147098603).

1221815221 is a wasteful number, since it uses less digits than its factorization.

1221815221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3002051.

The product of its digits is 640, while the sum is 25.

The square root of 1221815221 is about 34954.4735477449. The cubic root of 1221815221 is about 1069.0594176961.

Adding to 1221815221 its reverse (1225181221), we get a palindrome (2446996442).

The spelling of 1221815221 in words is "one billion, two hundred twenty-one million, eight hundred fifteen thousand, two hundred twenty-one".