%N Years of recorded appearances of Halley's Comet (negative years are B.C.).
%C 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
%H Joseph M. Laufer, <a href="http://www.lauferworld.com/haleyhome.html">Halley's Comet, Its 30th Recorded Return, 1985-1986</a>.
%e a(30) = 1985 because the 30th recorded appearance of Halley's comet was in 1985.
%Y See A072235 for another version.
%A _David Terr_, Jan 03 2005