4221
From Tardis Wiki, the free Doctor Who reference
the Year 43K2.1 (or 4,321) was the year in which the New British Empire sent the Walker Expedition into the vicinity of the Black hole K37J5 to find and retrieve the power source that was keeping the Planet Krop Tor in a stable orbit. (Tardisode 8, Tardisode 9. DW: The Impossible Planet, The Satan Pit)
