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# Trice sequence

The Trice sequence consists of the nine numbers 21, 36, 55, 60, 67, 68, 92, 93, 125 in ascending order. It was published in Clifford Pickover’s Mazes of the Mind in 1992 and added to the On-Line Encyclopedia of Integer Sequences early on in its history (see A001491), but for years people couldn’t figure out what the sequence was because most of them were searching for a mathematical explanation. The first three numbers are both triangular and hexagonal, but none of the following numbers are. According to Neil Sloane, “this was a mystery for many years; even Clifford Pickover could not recall the explanation .” It wasn’t until 1998 that Derek Holt identified the sequence and let Sloane know that it consists of the opus numbers of Beethoven’s nine symphonies.

## Mathematics Subject Classification

00A99*no label found*

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