1809721409 has 2 divisors, whose sum is σ = 1809721410. Its totient is φ = 1809721408.

The previous prime is 1809721373. The next prime is 1809721429. The reversal of 1809721409 is 9041279081.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1176695809 + 633025600 = 34303^2 + 25160^2 .

It is a cyclic number.

It is not a de Polignac number, because 1809721409 - 2⁸ = 1809721153 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (1809721429) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 904860704 + 904860705.

It is an arithmetic number, because the mean of its divisors is an integer number (904860705).

Almost surely, 2^1809721409 is an apocalyptic number.

It is an amenable number.

1809721409 is a deficient number, since it is larger than the sum of its proper divisors (1).

1809721409 is an equidigital number, since it uses as much as digits as its factorization.

1809721409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 36288, while the sum is 41.

The square root of 1809721409 is about 42540.8205021953. The cubic root of 1809721409 is about 1218.6263786108.

The spelling of 1809721409 in words is "one billion, eight hundred nine million, seven hundred twenty-one thousand, four hundred nine".