815172221 has 4 divisors (see below), whose sum is σ = 817300992. Its totient is φ = 813043452.

The previous prime is 815172217. The next prime is 815172227. The reversal of 815172221 is 122271518.

815172221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 815172221 - 2² = 815172217 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 (815172227) 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, 1063811 + ... + 1064576.

It is an arithmetic number, because the mean of its divisors is an integer number (204325248).

Almost surely, 2^815172221 is an apocalyptic number.

It is an amenable number.

815172221 is a deficient number, since it is larger than the sum of its proper divisors (2128771).

815172221 is a wasteful number, since it uses less digits than its factorization.

815172221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2128770.

The product of its digits is 2240, while the sum is 29.

The square root of 815172221 is about 28551.2210071654. The cubic root of 815172221 is about 934.1496538272.

It can be divided in two parts, 81517 and 2221, that added together give a palindrome (83738).

The spelling of 815172221 in words is "eight hundred fifteen million, one hundred seventy-two thousand, two hundred twenty-one".