How many Tetriminos are there?

How many Tetriminos are there?

There are five free tetrominoes, seven one-sided tetrominoes, and 19 fixed tetrominoes. The free tetrominoes are known as the T-tetromino, L-tetromino, skew tetromino, square tetromino, and straight tetromino, respectively. The shapes were popularized in the game Tetris, developed by Alexey Pajitnov in June 1985.

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