cp's OEIS Frontend

This sequence is not well-defined for many reasons (negative years are ill-defined; calendars change often, so when does a year begin?; what does "observed" mean?; what if the comet was observed both at the end of one year and at the beginning of another, as in 1985/1986?; etc.). - N. J. A. Sloane, Jun 24 2007

The first four terms given are years B.C., others are A.D. I do not know if these years necessarily coincide with actual years of perihelion. Some sources and these numbers indicate that the comet's period varies. These years are taken directly from the U.S. National Air and Space Museum link.