221531661 has 24 divisors (see below), whose sum is σ = 345454200. Its totient is φ = 135991296.

The previous prime is 221531627. The next prime is 221531669. The reversal of 221531661 is 166135122.

It can be written as a sum of positive squares in 4 ways, for example, as 46498761 + 175032900 = 6819^2 + 13230^2 .

It is not a de Polignac number, because 221531661 - 2⁷ = 221531533 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (221531669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 50425 + ... + 54641.

It is an arithmetic number, because the mean of its divisors is an integer number (14393925).

Almost surely, 2^221531661 is an apocalyptic number.

It is an amenable number.

221531661 is a deficient number, since it is larger than the sum of its proper divisors (123922539).

221531661 is a wasteful number, since it uses less digits than its factorization.

221531661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4685 (or 4682 counting only the distinct ones).

The product of its digits is 2160, while the sum is 27.

The square root of 221531661 is about 14883.9397002272. The cubic root of 221531661 is about 605.0787967400.

Adding to 221531661 its reverse (166135122), we get a palindrome (387666783).

The spelling of 221531661 in words is "two hundred twenty-one million, five hundred thirty-one thousand, six hundred sixty-one".