1999904561 has 2 divisors, whose sum is σ = 1999904562. Its totient is φ = 1999904560.

The previous prime is 1999904549. The next prime is 1999904677. The reversal of 1999904561 is 1654099991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1999788961 + 115600 = 44719^2 + 340^2 .

It is an emirp because it is prime and its reverse (1654099991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1999904561 - 2¹⁸ = 1999642417 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 (1999904521) 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 as a sum of consecutive naturals, namely, 999952280 + 999952281.

It is an arithmetic number, because the mean of its divisors is an integer number (999952281).

Almost surely, 2^1999904561 is an apocalyptic number.

It is an amenable number.

1999904561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1999904561 is an equidigital number, since it uses as much as digits as its factorization.

1999904561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 787320, while the sum is 53.

The square root of 1999904561 is about 44720.2924968073. The cubic root of 1999904561 is about 1259.9010086419.

The spelling of 1999904561 in words is "one billion, nine hundred ninety-nine million, nine hundred four thousand, five hundred sixty-one".