221332721 has 4 divisors (see below), whose sum is σ = 221366244. Its totient is φ = 221299200.

The previous prime is 221332687. The next prime is 221332763. The reversal of 221332721 is 127233122.

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 112360000 + 108972721 = 10600^2 + 10439^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-221332721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (221332421) 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 3 ways as a sum of consecutive naturals, for example, 3200 + ... + 21281.

It is an arithmetic number, because the mean of its divisors is an integer number (55341561).

Almost surely, 2^221332721 is an apocalyptic number.

It is an amenable number.

221332721 is a deficient number, since it is larger than the sum of its proper divisors (33523).

221332721 is an equidigital number, since it uses as much as digits as its factorization.

221332721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33522.

The product of its digits is 1008, while the sum is 23.

The square root of 221332721 is about 14877.2551567821. The cubic root of 221332721 is about 604.8976180827.

Adding to 221332721 its reverse (127233122), we get a palindrome (348565843).

The spelling of 221332721 in words is "two hundred twenty-one million, three hundred thirty-two thousand, seven hundred twenty-one".