1103

This number is a prime.

John Conway's game of life starts with cells that are "alive" (marked or shaded) in an infinite array. Each subsequent "generation" (iteration): a living cell stays alive if it has either two or three living neighbors; and a dead cell springs to life if it has exactly three live neighbors. The R-pentomino and its next four generations are shown in the figure above. The pattern that this pentomino generates does not stabilize until the 1103rd generation. (There is even an initial arrangement of cells that will generate the prime numbers!) [Caldwell]