History of the Pentomino Puzzle
Twelve pieces of five squares each: a puzzle published by Henry Dudeney in 1907, named "pentominoes" by Solomon Golomb in 1953.
Dudeney and Golomb
The earliest known puzzle with a complete set of the twelve pieces is in Henry Dudeney's book The Canterbury Puzzles from 1907. The name "pentomino" comes from the mathematician Solomon Golomb, who began to describe these shapes in 1953; the puzzle column of Martin Gardner in Scientific American made them widely known.
Counting the solutions
How many ways are there to fill 6 × 10? C. B. and Jenifer Haselgrove worked it out by computer in 1960: 2339, not counting turned or flipped copies of a whole solution. For 5 × 12 there are 1010, for 4 × 15 there are 368, and for 3 × 20 only 2.