221561665 has 8 divisors (see below), whose sum is σ = 286325928. Its totient is φ = 163614720.

The previous prime is 221561651. The next prime is 221561689. The reversal of 221561665 is 566165122.

It can be written as a sum of positive squares in 4 ways, for example, as 4765489 + 216796176 = 2183^2 + 14724^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 221561665 - 2¹¹ = 221559617 is a prime.

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 221561665.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1704256 + ... + 1704385.

It is an arithmetic number, because the mean of its divisors is an integer number (35790741).

Almost surely, 2^221561665 is an apocalyptic number.

It is an amenable number.

221561665 is a deficient number, since it is larger than the sum of its proper divisors (64764263).

221561665 is a wasteful number, since it uses less digits than its factorization.

221561665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3408659.

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

The square root of 221561665 is about 14884.9475981610. The cubic root of 221561665 is about 605.1061125717.

The spelling of 221561665 in words is "two hundred twenty-one million, five hundred sixty-one thousand, six hundred sixty-five".