15221221 has 2 divisors, whose sum is σ = 15221222. Its totient is φ = 15221220.

The previous prime is 15221207. The next prime is 15221231. The reversal of 15221221 is 12212251.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12348196 + 2873025 = 3514^2 + 1695^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-15221221 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 15221195 and 15221204.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (15221231) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7610610 + 7610611.

It is an arithmetic number, because the mean of its divisors is an integer number (7610611).

Almost surely, 2^15221221 is an apocalyptic number.

It is an amenable number.

15221221 is a deficient number, since it is larger than the sum of its proper divisors (1).

15221221 is an equidigital number, since it uses as much as digits as its factorization.

15221221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 80, while the sum is 16.

The square root of 15221221 is about 3901.4383245157. The cubic root of 15221221 is about 247.8276909657.

Adding to 15221221 its reverse (12212251), we get a palindrome (27433472).

The spelling of 15221221 in words is "fifteen million, two hundred twenty-one thousand, two hundred twenty-one".