1908728721 has 9 divisors (see below), whose sum is σ = 2757241929. Its totient is φ = 1272398436.

The previous prime is 1908728681. The next prime is 1908728743. The reversal of 1908728721 is 1278278091.

The square root of 1908728721 is 43689.

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

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

It is a de Polignac number, because none of the positive numbers 2^k-1908728721 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1908728791) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 123786 + ... + 138348.

Almost surely, 2^1908728721 is an apocalyptic number.

1908728721 is the 43689-th square number.

1908728721 is the 21845-th centered octagonal number.

It is an amenable number.

1908728721 is a deficient number, since it is larger than the sum of its proper divisors (848513208).

1908728721 is an frugal number, since it uses more digits than its factorization.

1908728721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29132 (or 14566 counting only the distinct ones).

The product of its (nonzero) digits is 112896, while the sum is 45.

The cubic root of 1908728721 is about 1240.4561106070.

Multiplying 1908728721 by its product of nonzero digits (112896), we get a square (215487837686016 = 14679504²).

The spelling of 1908728721 in words is "one billion, nine hundred eight million, seven hundred twenty-eight thousand, seven hundred twenty-one".