Found with PFGW Version 3.4.5

21^8766+20 is 2-PRP! (4.4216s+0.0047s)
21^8766+20 is 3-PRP! (3.8124s+0.0011s)
21^8766+20 is 5-PRP! (3.7427s+0.0011s)
21^8766+20 is 7-PRP! (3.6650s+0.0011s)
21^8766+20 is 11-PRP! (3.6216s+0.0011s)

Primality testing 21^8766+20 [N-1/N+1, Brillhart-Lehmer-Selfridge]
Running N-1 test using base 2
Running N+1 test using discriminant 7, base 2+sqrt(7)
Calling N+1 BLS with factored part 0.10% and helper 0.01% (0.31% proof)
21^8766+20 is Fermat and Lucas PRP! (20.5986s+0.0034s)

To be completed...