221916721 has 4 divisors (see below), whose sum is σ = 238987252. Its totient is φ = 204846192.

The previous prime is 221916707. The next prime is 221916727. The reversal of 221916721 is 127619122.

221916721 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, and also an emirpimes, since its reverse is a distinct semiprime: 127619122 = 2 ⋅63809561.

It can be written as a sum of positive squares in 2 ways, for example, as 30371121 + 191545600 = 5511^2 + 13840^2 .

It is a cyclic number.

It is not a de Polignac number, because 221916721 - 2⁵ = 221916689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (221916727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8535246 + ... + 8535271.

It is an arithmetic number, because the mean of its divisors is an integer number (59746813).

Almost surely, 2^221916721 is an apocalyptic number.

It is an amenable number.

221916721 is a deficient number, since it is larger than the sum of its proper divisors (17070531).

221916721 is a wasteful number, since it uses less digits than its factorization.

221916721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17070530.

The product of its digits is 3024, while the sum is 31.

The square root of 221916721 is about 14896.8695033554. The cubic root of 221916721 is about 605.4291707039.

The spelling of 221916721 in words is "two hundred twenty-one million, nine hundred sixteen thousand, seven hundred twenty-one".