815558221 has 4 divisors (see below), whose sum is σ = 863532252. Its totient is φ = 767584192.

The previous prime is 815558201. The next prime is 815558251. The reversal of 815558221 is 122855518.

815558221 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 an emirpimes, since its reverse is a distinct semiprime: 122855518 = 2 ⋅61427759.

It can be written as a sum of positive squares in 2 ways, for example, as 539632900 + 275925321 = 23230^2 + 16611^2 .

It is a cyclic number.

It is not a de Polignac number, because 815558221 - 2²¹ = 813461069 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 (815558201) 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, 23986990 + ... + 23987023.

It is an arithmetic number, because the mean of its divisors is an integer number (215883063).

Almost surely, 2^815558221 is an apocalyptic number.

It is an amenable number.

815558221 is a deficient number, since it is larger than the sum of its proper divisors (47974031).

815558221 is a wasteful number, since it uses less digits than its factorization.

815558221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 47974030.

The product of its digits is 32000, while the sum is 37.

The square root of 815558221 is about 28557.9799880874. The cubic root of 815558221 is about 934.2970766081.

The spelling of 815558221 in words is "eight hundred fifteen million, five hundred fifty-eight thousand, two hundred twenty-one".