187991521 has 3 divisors (see below), whose sum is σ = 188005233. Its totient is φ = 187977810.

The previous prime is 187991449. The next prime is 187991539. The reversal of 187991521 is 125199781.

The square root of 187991521 is 13711.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 187991521 - 2⁹ = 187991009 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (187991591) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 6856 + ... + 20566.

It is an arithmetic number, because the mean of its divisors is an integer number (62668411).

Almost surely, 2^187991521 is an apocalyptic number.

187991521 is the 13711-st square number.

187991521 is the 6856-th centered octagonal number.

It is an amenable number.

187991521 is a deficient number, since it is larger than the sum of its proper divisors (13712).

187991521 is an frugal number, since it uses more digits than its factorization.

187991521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27422 (or 13711 counting only the distinct ones).

The product of its digits is 45360, while the sum is 43.

The cubic root of 187991521 is about 572.8568191886.

The spelling of 187991521 in words is "one hundred eighty-seven million, nine hundred ninety-one thousand, five hundred twenty-one".