171720345932521 has 9 divisors (see below), whose sum is σ = 175452336286231. Its totient is φ = 168066118757272.

The previous prime is 171720345932491. The next prime is 171720345932557. The reversal of 171720345932521 is 125239543027171.

The square root of 171720345932521 is 13104211.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 3188956635225 + 168531389297296 = 1785765^2 + 12981964^2 .

It is not a de Polignac number, because 171720345932521 - 2¹¹ = 171720345930473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (171720345932221) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 615758511 + ... + 616037323.

Almost surely, 2^{171720345932521} is an apocalyptic number.

171720345932521 is the 13104211-st square number.

171720345932521 is the 6552106-th centered octagonal number.

It is an amenable number.

171720345932521 is a deficient number, since it is larger than the sum of its proper divisors (3731990353710).

171720345932521 is an frugal number, since it uses more digits than its factorization.

171720345932521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 557720 (or 278860 counting only the distinct ones).

The product of its (nonzero) digits is 3175200, while the sum is 52.

Adding to 171720345932521 its reverse (125239543027171), we get a palindrome (296959888959692).

The spelling of 171720345932521 in words is "one hundred seventy-one trillion, seven hundred twenty billion, three hundred forty-five million, nine hundred thirty-two thousand, five hundred twenty-one".