15121221 has 4 divisors (see below), whose sum is σ = 20161632. Its totient is φ = 10080812.

The previous prime is 15121213. The next prime is 15121231. The reversal of 15121221 is 12212151.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 15121221 - 2³ = 15121213 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 15121221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15121201) 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, 2520201 + ... + 2520206.

It is an arithmetic number, because the mean of its divisors is an integer number (5040408).

Almost surely, 2^15121221 is an apocalyptic number.

It is an amenable number.

15121221 is a deficient number, since it is larger than the sum of its proper divisors (5040411).

15121221 is an equidigital number, since it uses as much as digits as its factorization.

15121221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5040410.

The product of its digits is 40, while the sum is 15.

The square root of 15121221 is about 3888.6014195338. The cubic root of 15121221 is about 247.2837740122.

Adding to 15121221 its reverse (12212151), we get a palindrome (27333372).

The spelling of 15121221 in words is "fifteen million, one hundred twenty-one thousand, two hundred twenty-one".