187128721 has 8 divisors (see below), whose sum is σ = 206970344. Its totient is φ = 168065280.

The previous prime is 187128719. The next prime is 187128731. The reversal of 187128721 is 127821781.

It can be written as a sum of positive squares in 4 ways, for example, as 68558400 + 118570321 = 8280^2 + 10889^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 187128721 - 2¹ = 187128719 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is the 13680-th Hogben number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (187128731) by changing a digit.

It is a nontrivial repunit in base 13679.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 194040 + ... + 195001.

It is an arithmetic number, because the mean of its divisors is an integer number (25871293).

Almost surely, 2^187128721 is an apocalyptic number.

It is an amenable number.

187128721 is a deficient number, since it is larger than the sum of its proper divisors (19841623).

187128721 is a wasteful number, since it uses less digits than its factorization.

187128721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 389091.

The product of its digits is 12544, while the sum is 37.

The square root of 187128721 is about 13679.5000274133. The cubic root of 187128721 is about 571.9790864360.

The spelling of 187128721 in words is "one hundred eighty-seven million, one hundred twenty-eight thousand, seven hundred twenty-one".