171216721 has 8 divisors (see below), whose sum is σ = 184804200. Its totient is φ = 157688832.

The previous prime is 171216679. The next prime is 171216743. The reversal of 171216721 is 127612171.

It can be written as a sum of positive squares in 4 ways, for example, as 28772496 + 142444225 = 5364^2 + 11935^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 171216721 - 2⁷ = 171216593 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 171216721.

It is not an unprimeable number, because it can be changed into a prime (171216781) 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 7 ways as a sum of consecutive naturals, for example, 8830 + ... + 20503.

It is an arithmetic number, because the mean of its divisors is an integer number (23100525).

Almost surely, 2^171216721 is an apocalyptic number.

It is an amenable number.

171216721 is a deficient number, since it is larger than the sum of its proper divisors (13587479).

171216721 is a wasteful number, since it uses less digits than its factorization.

171216721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29795.

The product of its digits is 1176, while the sum is 28.

The square root of 171216721 is about 13084.9807412927. The cubic root of 171216721 is about 555.2842966254.

Adding to 171216721 its reverse (127612171), we get a palindrome (298828892).

The spelling of 171216721 in words is "one hundred seventy-one million, two hundred sixteen thousand, seven hundred twenty-one".