19866638809 has 2 divisors, whose sum is σ = 19866638810. Its totient is φ = 19866638808.

The previous prime is 19866638807. The next prime is 19866638833. The reversal of 19866638809 is 90883666891.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18714240000 + 1152398809 = 136800^2 + 33947^2 .

It is a cyclic number.

It is not a de Polignac number, because 19866638809 - 2¹ = 19866638807 is a prime.

Together with 19866638807, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (19866638807) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9933319404 + 9933319405.

It is an arithmetic number, because the mean of its divisors is an integer number (9933319405).

Almost surely, 2^19866638809 is an apocalyptic number.

It is an amenable number.

19866638809 is a deficient number, since it is larger than the sum of its proper divisors (1).

19866638809 is an equidigital number, since it uses as much as digits as its factorization.

19866638809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 26873856, while the sum is 64.

The spelling of 19866638809 in words is "nineteen billion, eight hundred sixty-six million, six hundred thirty-eight thousand, eight hundred nine".