221615665 has 4 divisors (see below), whose sum is σ = 265938804. Its totient is φ = 177292528.

The previous prime is 221615659. The next prime is 221615687. The reversal of 221615665 is 566516122.

221615665 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.

It can be written as a sum of positive squares in 2 ways, for example, as 35129329 + 186486336 = 5927^2 + 13656^2 .

It is a cyclic number.

It is not a de Polignac number, because 221615665 - 2³ = 221615657 is a prime.

It is a super-2 number, since 2×221615665² = 98227005946784450, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 221615665.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22161562 + ... + 22161571.

It is an arithmetic number, because the mean of its divisors is an integer number (66484701).

Almost surely, 2^221615665 is an apocalyptic number.

It is an amenable number.

221615665 is a deficient number, since it is larger than the sum of its proper divisors (44323139).

221615665 is an equidigital number, since it uses as much as digits as its factorization.

221615665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44323138.

The product of its digits is 21600, while the sum is 34.

The square root of 221615665 is about 14886.7614006539. The cubic root of 221615665 is about 605.1552683012.

The spelling of 221615665 in words is "two hundred twenty-one million, six hundred fifteen thousand, six hundred sixty-five".