The nightmare of all Conway's Life first-time players. It only stabilizes into a two-tick oscillator after 1103 ticks, leaving around it a cloud of scattered gliders, blinkers and blocks. The first ones to stabilish the result were Gary Filipski and Brad Morgan, from Case Western Reserve University. (without computers.)
 OO
OO
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The r-pentomino is, of course, a Methuselah.