221815566729 has 27 divisors (see below), whose sum is σ = 329371396263. Its totient is φ = 143846457552.

The previous prime is 221815566703. The next prime is 221815566781. The reversal of 221815566729 is 927665518122.

The square root of 221815566729 is 470973.

It is a perfect power (a square), and thus also a powerful number.

221815566729 is a `hidden beast` number, since 2 + 2 + 1 + 8 + 1 + 5 + 566 + 72 + 9 = 666.

It can be written as a sum of positive squares in only one way, i.e., 198483615225 + 23331951504 = 445515^2 + 152748^2 .

It is not a de Polignac number, because 221815566729 - 2⁷ = 221815566601 is a prime.

It is not an unprimeable number, because it can be changed into a prime (221815566029) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 52275882 + ... + 52280124.

Almost surely, 2^221815566729 is an apocalyptic number.

221815566729 is the 470973-rd square number.

221815566729 is the 235487-th centered octagonal number.

It is an amenable number.

221815566729 is a deficient number, since it is larger than the sum of its proper divisors (107555829534).

221815566729 is an frugal number, since it uses more digits than its factorization.

221815566729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8566 (or 4283 counting only the distinct ones).

The product of its digits is 3628800, while the sum is 54.

It can be divided in two parts, 221815 and 566729, that added together give a square (788544 = 888²).

The spelling of 221815566729 in words is "two hundred twenty-one billion, eight hundred fifteen million, five hundred sixty-six thousand, seven hundred twenty-nine".