linear resistor values series?
The E12 series isn't quite evenly spaced from an exponential standpoint.

1.0 1.2 1.5 2.2 2.7 3.3 3.9 4.7 5.1 5.6 6.8 8.2

For example, 10/3.3 is much closer to 3 than to 3.3.  It is admittedly curious that the 12-per-decade series offers two ways of getting a 3:1 ratio within 1.3% (one is 10/3.3; the other is 8.2/2.7) but the best 2:1 ratios it offers are off by 3% or more (5.6/2.7 is 3.7% off; 6.8/3.3 is 3.03% off).  On the other hand, since the E12 series is typically used with 10%-tolerance parts, the sloppiness of the ratios doesn't really matter.

The E24 series (5% parts) offers values of 2.0 and 3.0; the E96 and E192 series offer 2.00, but the closest they offer to 3.0 is 3.01.