I'm looking for an instance of a prime for numbers of the form (10^n 78880-1)/3, where n is a positive integer. As a preliminary, it may be noted that n must be a multiple of 12. There are many other constraints based on division by small factors but since PrimeQ has a built-in small-factor trial-division subroutine, ultimately I am interested in those n that escape that subroutine, i.e. n where PrimeQ[(10^n 78880-1)/3] takes more than a second or so to evaluate. For example, the numbers 10008, 10032, 10068, 10140, 10188, 10320, 10332, 10368, 10392, 10404, 10584, 10608, 10620, 10644, 10692, 10764, 10824, 10872, 10932, 10980, 11004, ... I'd like to extend that list to, say, 10^6. How do I interrupt an evaluation that is taking too long so that I might move on to another candidate?