The number 1615201561 has the same digits as the 6th row of Pascal's triangle.

PFGW Version 1.2.0 for Windows [FFT v23.8]

Primality testing 10^11939+1615201561 [N-1/N+1, Brillhart-Lehmer-Selfridge]
Running N-1 test using base 3
Running N-1 test using base 7
Running N+1 test using discriminant 17, base 6+sqrt(17)
Running N+1 test using discriminant 17, base 13+sqrt(17)
Running N+1 test using discriminant 17, base 14+sqrt(17)
Running N+1 test using discriminant 17, base 17+sqrt(17)
10^11939+1615201561 is Fermat and Lucas PRP!

To be completed...