191878165521 has 135 divisors (see below), whose sum is σ = 355065401889. Its totient is φ = 102942669312.

The previous prime is 191878165463. The next prime is 191878165529. The reversal of 191878165521 is 125561878191.

The square root of 191878165521 is 438039.

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

191878165521 is a `hidden beast` number, since 1 + 9 + 1 + 8 + 7 + 81 + 6 + 552 + 1 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 95490270225 + 96387895296 = 309015^2 + 310464^2 .

It is not a de Polignac number, because 191878165521 - 2⁹ = 191878165009 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (191878165529) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 134 ways as a sum of consecutive naturals, for example, 469139565 + ... + 469139973.

Almost surely, 2^191878165521 is an apocalyptic number.

191878165521 is the 438039-th square number.

191878165521 is the 219020-th centered octagonal number.

It is an amenable number.

191878165521 is a deficient number, since it is larger than the sum of its proper divisors (163187236368).

191878165521 is an frugal number, since it uses more digits than its factorization.

191878165521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 878 (or 436 counting only the distinct ones).

The product of its digits is 1209600, while the sum is 54.

The spelling of 191878165521 in words is "one hundred ninety-one billion, eight hundred seventy-eight million, one hundred sixty-five thousand, five hundred twenty-one".