1687173721 has 4 divisors (see below), whose sum is σ = 1786419252. Its totient is φ = 1587928192.

The previous prime is 1687173703. The next prime is 1687173727. The reversal of 1687173721 is 1273717861.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1219057225 + 468116496 = 34915^2 + 21636^2 .

It is a cyclic number.

It is not a de Polignac number, because 1687173721 - 2⁹ = 1687173209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1687173727) 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 3 ways as a sum of consecutive naturals, for example, 49622740 + ... + 49622773.

It is an arithmetic number, because the mean of its divisors is an integer number (446604813).

Almost surely, 2^1687173721 is an apocalyptic number.

It is an amenable number.

1687173721 is a deficient number, since it is larger than the sum of its proper divisors (99245531).

1687173721 is an equidigital number, since it uses as much as digits as its factorization.

1687173721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 99245530.

The product of its digits is 98784, while the sum is 43.

The square root of 1687173721 is about 41075.2202793850. The cubic root of 1687173721 is about 1190.4740528262.

The spelling of 1687173721 in words is "one billion, six hundred eighty-seven million, one hundred seventy-three thousand, seven hundred twenty-one".