171985213521 has 135 divisors (see below), whose sum is σ = 291365905369. Its totient is φ = 101023599600.

The previous prime is 171985213511. The next prime is 171985213523. The reversal of 171985213521 is 125312589171.

The square root of 171985213521 is 414711.

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

171985213521 is a `hidden beast` number, since 1 + 7 + 1 + 98 + 521 + 35 + 2 + 1 = 666.

It is not a de Polignac number, because 171985213521 - 2⁵ = 171985213489 is a prime.

It is a super-2 number, since 2×171985213521² (a number of 23 digits) contains 22 as substring.

Its product of digits (151200) is a multiple of the sum of its prime divisors (144).

It is not an unprimeable number, because it can be changed into a prime (171985213523) by changing a digit.

It is a polite number, since it can be written in 134 ways as a sum of consecutive naturals, for example, 2422326916 + ... + 2422326986.

Almost surely, 2^171985213521 is an apocalyptic number.

171985213521 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

171985213521 is the 414711-st square number.

171985213521 is the 207356-th centered octagonal number.

It is an amenable number.

171985213521 is a deficient number, since it is larger than the sum of its proper divisors (119380691848).

171985213521 is an frugal number, since it uses more digits than its factorization.

171985213521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 294 (or 144 counting only the distinct ones).

The product of its digits is 151200, while the sum is 45.

The spelling of 171985213521 in words is "one hundred seventy-one billion, nine hundred eighty-five million, two hundred thirteen thousand, five hundred twenty-one".