This is a PRP value of the Ramanujan Tau function.
http://dx.doi.org/10.1007/s11139-012-9420-8

Verified with PFGW (v3.7.8) and Pari/GP (v2.5.5).

lucasU(85753393288710,594149321766565107986044015109,18947) is 3-PRP! (2005.8784s+0.0172s)

To be completed...