19187721809 has 2 divisors, whose sum is σ = 19187721810. Its totient is φ = 19187721808.

The previous prime is 19187721797. The next prime is 19187721869. The reversal of 19187721809 is 90812778191.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18343993600 + 843728209 = 135440^2 + 29047^2 .

It is a cyclic number.

It is not a de Polignac number, because 19187721809 - 2²⁴ = 19170944593 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 (19187721869) 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 as a sum of consecutive naturals, namely, 9593860904 + 9593860905.

It is an arithmetic number, because the mean of its divisors is an integer number (9593860905).

Almost surely, 2^19187721809 is an apocalyptic number.

It is an amenable number.

19187721809 is a deficient number, since it is larger than the sum of its proper divisors (1).

19187721809 is an equidigital number, since it uses as much as digits as its factorization.

19187721809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 508032, while the sum is 53.

The spelling of 19187721809 in words is "nineteen billion, one hundred eighty-seven million, seven hundred twenty-one thousand, eight hundred nine".