68 -

68 is a "happy number," meaning that if you take the sum of the squares of its digits and continue the process, you eventually reach 1. The Last Two-Digit "First" Number: In the digits of

, 68 is the very last two-digit number to appear for the first time. 68 is a "happy number," meaning that if

While 69 often gets the attention, mathematicians and number theorists find 68 far more compelling for several reasons. It is known as the largest number that

It is known as the largest number that can be expressed as the sum of two primes in exactly two different ways ( 68 is a "happy number

In restaurant slang, "68" is the opposite of "86" (which means to remove an item from the menu). A "68" means an item is back on the menu or available.

On an infinite chessboard, there are 68 distinct squares that are exactly three knight's moves away from any starting square.