19685817817 has 2 divisors, whose sum is σ = 19685817818. Its totient is φ = 19685817816.

The previous prime is 19685817791. The next prime is 19685817821. The reversal of 19685817817 is 71871858691.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18462287376 + 1223530441 = 135876^2 + 34979^2 .

It is an emirp because it is prime and its reverse (71871858691) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19685817817 - 2²³ = 19677429209 is a prime.

It is a super-2 number, since 2×19685817817² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (19685817317) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9842908908 + 9842908909.

It is an arithmetic number, because the mean of its divisors is an integer number (9842908909).

Almost surely, 2^19685817817 is an apocalyptic number.

It is an amenable number.

19685817817 is a deficient number, since it is larger than the sum of its proper divisors (1).

19685817817 is an equidigital number, since it uses as much as digits as its factorization.

19685817817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6773760, while the sum is 61.

The spelling of 19685817817 in words is "nineteen billion, six hundred eighty-five million, eight hundred seventeen thousand, eight hundred seventeen".