From: David Wilson <davidwwilson@comcast.net>

What is the smallest value a(d) such that every d-digit sequence occurs in the decimal expansion of 1/d (after the decimal point).

For small d >= 1 my program says

17, 109, 1019, 10007, 100019, ...

but it seems stuck on 6 digits, so perhaps there is an overflow issue.

1000171 ought to work. I cannot convince myself that the smallest /unique prime/ > 10^d is the minimal value that satisfies the condition, but it certainly matches the 5 values you've found so far. Phil