Found with PFGW Version 3.4.6

21^12597-20 is 2-PRP! (8.8371s+0.0064s)
21^12597-20 is 3-PRP! (8.2891s+0.0078s)
21^12597-20 is 5-PRP! (8.3260s+0.0079s)
21^12597-20 is 7-PRP! (8.7691s+0.0048s)
21^12597-20 is 11-PRP! (8.4690s+0.0079s)

Primality testing 21^12597-20 [N-1/N+1, Brillhart-Lehmer-Selfridge]
Running N-1 test using base 23
Running N-1 test using base 29
Running N-1 test using base 41
Running N-1 test using base 47
Running N-1 test using base 53
Running N+1 test using discriminant 71, base 5+sqrt(71)
Calling N-1 BLS with factored part 0.24% and helper 0.05% (0.78% proof)
21^12597-20 is Fermat and Lucas PRP! (166.7054s+0.0114s)

To be completed...