1997821809 has 27 divisors (see below), whose sum is σ = 2957778187. Its totient is φ = 1299431184.

The previous prime is 1997821799. The next prime is 1997821811. The reversal of 1997821809 is 9081287991.

The square root of 1997821809 is 44697.

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

It can be written as a sum of positive squares in only one way, i.e., 111830625 + 1885991184 = 10575^2 + 43428^2 .

It is not a de Polignac number, because 1997821809 - 2²⁵ = 1964267377 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1997821829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 6302119 + ... + 6302435.

Almost surely, 2^1997821809 is an apocalyptic number.

1997821809 is the 44697-th square number.

1997821809 is the 22349-th centered octagonal number.

It is an amenable number.

1997821809 is a deficient number, since it is larger than the sum of its proper divisors (959956378).

1997821809 is an frugal number, since it uses more digits than its factorization.

1997821809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 734 (or 367 counting only the distinct ones).

The product of its (nonzero) digits is 653184, while the sum is 54.

The cubic root of 1997821809 is about 1259.4634922981.

The spelling of 1997821809 in words is "one billion, nine hundred ninety-seven million, eight hundred twenty-one thousand, eight hundred nine".