Baltimore — IN 1975, a San Diego woman named Marjorie Rice read in her son’s Scientific American magazine that there were only eight known pentagonal shapes that could entirely tile, or tessellate, a plane. Despite having had no math beyond high school, she resolved to find another. By 1977, she’d discovered not just one but four new tessellations — a result noteworthy enough to be published the following year in a mathematics journal.

The article that turned Ms. Rice into an amateur researcher was by the legendary polymath Martin Gardner. His “Mathematical Games” series, which ran in Scientific American for more than 25 years, introduced millions worldwide to the joys of recreational mathematics. I read him in Mumbai as an undergraduate, and even dug up his original 1956 column on “hexaflexagons” (folded paper hexagons that can be flexed to reveal different flowerlike faces) to construct some myself.

“Recreational math” might sound like an oxymoron to some, but the term can broadly include such immensely popular puzzles as Sudoku and KenKen, in addition to various games and brain teasers. The qualifying characteristics are that no advanced mathematical knowledge like calculus be required, and the activity engage enough of the same logical and deductive skills used in mathematics.

Unlike Sudoku, which always has the same format and gets easier with practice, the disparate puzzles that Mr. Gardner favored required different, inventive techniques to crack. The solution in such puzzles usually pops up in its entirety, through a flash of insight, rather than emerging steadily via step-by-step deduction as in Sudoku. An example: How can you identify a single counterfeit penny, slightly lighter than the rest, from a group of nine, in only two weighings?