This number is a composite.
Just showing those entries submitted by 'Carmichael': (Click here to show all)
18854317021 = 197 * 421 * 463 * 491. This is the first 4-brilliant Carmichael number whose prime factors are 3-digits in length. Note that it truncates on one side to the prime 18854317, and on the other side to the prime 854317021. [Carmichael]