I can fit a cubic to these dates. A curve, ax3+bx2+cx+d. And, as a result, I can extrapolate to determine the next date.
It's 2013. That can't be right. I went earlier today.
If I start with 1977, 1986, 1991, 1998 and 2005 I have to use a quartic, and the next number in the series is 2002. Does anyone have a time machine?