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(-21487665696030828,723455010776824500718948741505171,15739) is 3-PRP! (1726.1023s+0.0161s)

To be completed...