171721721 has 2 divisors, whose sum is σ = 171721722. Its totient is φ = 171721720.

The previous prime is 171721687. The next prime is 171721723. The reversal of 171721721 is 127127171.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 144264121 + 27457600 = 12011^2 + 5240^2 .

It is a cyclic number.

It is not a de Polignac number, because 171721721 - 2¹⁰ = 171720697 is a prime.

Together with 171721723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (171721723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 85860860 + 85860861.

It is an arithmetic number, because the mean of its divisors is an integer number (85860861).

Almost surely, 2^171721721 is an apocalyptic number.

It is an amenable number.

171721721 is a deficient number, since it is larger than the sum of its proper divisors (1).

171721721 is an equidigital number, since it uses as much as digits as its factorization.

171721721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1372, while the sum is 29.

The square root of 171721721 is about 13104.2634665211. The cubic root of 171721721 is about 555.8296937550.

Adding to 171721721 its reverse (127127171), we get a palindrome (298848892).

The spelling of 171721721 in words is "one hundred seventy-one million, seven hundred twenty-one thousand, seven hundred twenty-one".