I'm a newbie to the forum, so be nice to me

I was trying to write some Python script to calculate resistor values, and wanted to automatically generate lists of the preferred ranges of resistor values (E6, E12, E24 etc.).

From what I've been able to find by reading & Googling, the "E series" are logarithmic series / geometric series in which each decade is divided into E values, and the value of its n-th member may be calculated using the formula:

10^(n/E)

So for the E12 series, this should give values (with rounding & to 2 sig figures) of:

10,12,15,18,22,26,32,38,46,56,68,83

However, the E12 series for resistors actually goes:

10,12,15,18,22,

**27,33,39,47,**56,68,

**82**

What is the reason for the discrepancy?

Is it a quirk of history, or do I need to check my sums?

Many thanks in anticipation

Dave

(Swansea,UK)