PRP in base 59 and 61 For (85^n-83^n)/2, I found hitherto: (85^3-83^3)/2 (85^11-83^11)/2 (85^23-83^23)/2 (85^29-83^29)/2 (85^71-83^71)/2 (85^12763-83^12763)/2 (85^17387-83^17387)/2
To be completed...