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(372215 spells 'SIZZLE' when turned upside down on a calculator.)

PFGW Version 1.2.0 for Windows [FFT v23.8]

Primality testing 10^21173+372215001
[N-1/N+1, Brillhart-Lehmer-Selfridge]
Running N-1 test using base 13
Running N+1 test using discriminant 31, base 22+sqrt(31)
10^21173+372215001 is Fermat and Lucas PRP!

To be completed...