1686005721 has 9 divisors (see below), whose sum is σ = 2435519541. Its totient is φ = 1123921692.

The previous prime is 1686005701. The next prime is 1686005723. The reversal of 1686005721 is 1275006861.

The square root of 1686005721 is 41061.

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

1686005721 is a `hidden beast` number, since 1 + 6 + 86 + 0 + 0 + 572 + 1 = 666.

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 1686005721 - 2¹³ = 1685997529 is a prime.

It is a zygodrome in base 3.

It is not an unprimeable number, because it can be changed into a prime (1686005723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 116340 + ... + 130026.

Almost surely, 2^1686005721 is an apocalyptic number.

1686005721 is the 41061-st square number.

1686005721 is the 20531-st centered octagonal number.

It is an amenable number.

1686005721 is a deficient number, since it is larger than the sum of its proper divisors (749513820).

1686005721 is an frugal number, since it uses more digits than its factorization.

1686005721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27380 (or 13690 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 36.

The cubic root of 1686005721 is about 1190.1992748219.

Multiplying 1686005721 by its sum of digits (36), we get a square (60696205956 = 246366²).

The spelling of 1686005721 in words is "one billion, six hundred eighty-six million, five thousand, seven hundred twenty-one".