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 2020-06-09, 22:09 #255 carpetpool     "Sam" Nov 2016 22·79 Posts k*b^n+-1 with k < n? Also another interesting problem if anyone's interested: Twin primes of the form k*b^n+-1 with k < n --> Due to the limited choices of fixing only base b, there are extremely rare. I tested some bases (3, 5, 6, 7, 10, 11, 12). Here are the largest twins found to n=2K (except b=3, which is checked to n=10K). Quite small, I tell you: Second twin (p+2): Code: 2618*3^4286+1 336*5^765+1 613*6^1922+1 525*10^632+1 1182*11^1409+1 860*12^967+1 I didn't find any for base 7, although I'm sure they exist. The idea is that if k < n, we can get k as small as possible, so if all bases < 100 were tested, odds are you'll find a twin with a very small k. Continuing on with the search. Last fiddled with by carpetpool on 2020-06-09 at 22:10