Found with PFGW Version 3.5.2

77^8473-76 is 2-PRP! (14.8655s+0.0164s)
77^8473-76 is 3-PRP! (17.7436s+0.0065s)
77^8473-76 is 5-PRP! (19.3307s+0.0147s)
77^8473-76 is 7-PRP! (18.3240s+0.0067s)
77^8473-76 is 11-PRP! (18.1950s+0.0072s)

Primality testing 77^8473-76 [N-1/N+1, Brillhart-Lehmer-Selfridge]
Running N-1 test using base 23
Running N+1 test using discriminant 31, base 10+sqrt(31)
Calling N-1 BLS with factored part 0.26% and helper 0.04% (0.81% proof)
77^8473-76 is Fermat and Lucas PRP! (129.3825s+0.0197s)

To be completed...