Searched up to 24000.

(5379919 spells 'GIGGLES' when turned upside down on a calculator.)

PFGW Version 1.2.0 for Windows [FFT v23.8]

Primality testing 10^15423+5379919
[N-1/N+1, Brillhart-Lehmer-Selfridge]
Running N-1 test using base 11
Running N+1 test using discriminant 19, base 1+sqrt(19)
Running N+1 test using discriminant 19, base 2+sqrt(19)
Running N+1 test using discriminant 19, base 3+sqrt(19)
10^15423+5379919 is Fermat and Lucas PRP!

To be completed...