12215721 has 8 divisors (see below), whose sum is σ = 18614464. Its totient is φ = 6980400.

The previous prime is 12215713. The next prime is 12215743. The reversal of 12215721 is 12751221.

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

It is not a de Polignac number, because 12215721 - 2³ = 12215713 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21), and also a Moran number because the ratio is a prime number: 581701 = 12215721 / (1 + 2 + 2 + 1 + 5 + 7 + 2 + 1).

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (12215701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 290830 + ... + 290871.

It is an arithmetic number, because the mean of its divisors is an integer number (2326808).

Almost surely, 2^12215721 is an apocalyptic number.

It is an amenable number.

12215721 is a deficient number, since it is larger than the sum of its proper divisors (6398743).

12215721 is an equidigital number, since it uses as much as digits as its factorization.

12215721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 581711.

The product of its digits is 280, while the sum is 21.

The square root of 12215721 is about 3495.0995693971. The cubic root of 12215721 is about 230.3065917594.

Adding to 12215721 its reverse (12751221), we get a palindrome (24966942).

The spelling of 12215721 in words is "twelve million, two hundred fifteen thousand, seven hundred twenty-one".