Found with PFGW Version 3.4.8

27^15221-26 is 2-PRP! (22.8698s+0.0021s)
27^15221-26 is 3-PRP! (23.3047s+0.0022s)
27^15221-26 is 5-PRP! (21.5227s+0.0024s)
27^15221-26 is 7-PRP! (19.1870s+0.0021s)
27^15221-26 is 11-PRP! (22.4407s+0.0022s)

Primality testing 27^15221-26 [N-1/N+1, Brillhart-Lehmer-Selfridge]
Running N-1 test using base 17
Running N+1 test using discriminant 29, base 16+sqrt(29)
Calling N-1 BLS with factored part 0.38% and helper 0.02% (1.14% proof)
27^15221-26 is Fermat and Lucas PRP! (142.6096s+0.0085s)

To be completed...