Randall Munroe’s xkcd has a table of slightly wrong equations and identities.
The table gives that the number of seconds in a year is 754 = 31640625 or (using the “RENT method”) 525,600 × 60 = 31536000. (This refers to the song Seasons of Love, which features the number of minutes in a year prominently in its lyrics.) I’ve always been partial to “pi seconds is a nanocentury” (attributed to Tom Duff), which gives π × 107 for the number of seconds in a year, but you have to know π for this to be useful.
Also, while I’m on the subject: it’s easy to remember that the circumference of the Earth is 4 × 107 meters, or 40,000 kilometers; the meter was originally defined to be one ten-millionth of the distance from the North Pole to the equator through Paris. Call this C, or 2πr. The surface area of the Earth is therefore 4πr2 = C2/π, which works out to (1.6/π) × 1014 square meters; may as well let π = 3.2 for the moment and call that 5 × 1013. Munroe gives 698, which I suppose has some amusement value.