Parametric Array Formula

[shelmsGYSXD]

I have a simple question, I think my brain is just fried from the long week. I am trying to do a parametric array with some holes and I just need help with my formula. Here's what you need to know, when the Length is 1' the Array should be 3, when the Length is 2' the Array should be 7, when the Length is 4' the Array should be 15, when the Length is 6' the Array should be 23, and when the Length is 8' the Array should be 31. What formula will turn out these numbers for me?

[mhiserZFHXS · Accepted solution]

(Length*4) - 1

Actually, you'll need to get rid of the units, so:

((Length/1)*4) - 1

[ToanDN · Accepted solution]

(Length/3")-1

[shelmsGYSXD]

That second one works perfectly, thank you!