166891388636025 has 135 divisors (see below), whose sum is σ = 312173060310111. Its totient is φ = 88144018184160.

The previous prime is 166891388635957. The next prime is 166891388636057. The reversal of 166891388636025 is 520636883198661.

The square root of 166891388636025 is 12918645.

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

166891388636025 is a `hidden beast` number, since 1 + 6 + 6 + 8 + 9 + 1 + 3 + 8 + 8 + 6 + 3 + 602 + 5 = 666.

It can be written as a sum of positive squares in only one way, i.e., 60080899908969 + 106810488727056 = 7751187^2 + 10334916^2 .

It is a tau number, because it is divible by the number of its divisors (135).

It is not a de Polignac number, because 166891388636025 - 2¹⁵ = 166891388603257 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 134 ways as a sum of consecutive naturals, for example, 62203274334 + ... + 62203277016.

Almost surely, 2^{166891388636025} is an apocalyptic number.

166891388636025 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

166891388636025 is the 12918645-th square number.

166891388636025 is the 6459323-rd centered octagonal number.

It is an amenable number.

166891388636025 is a deficient number, since it is larger than the sum of its proper divisors (145281671674086).

166891388636025 is an frugal number, since it uses more digits than its factorization.

166891388636025 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5602 (or 2798 counting only the distinct ones).

The product of its (nonzero) digits is 537477120, while the sum is 72.

The spelling of 166891388636025 in words is "one hundred sixty-six trillion, eight hundred ninety-one billion, three hundred eighty-eight million, six hundred thirty-six thousand, twenty-five".