Can anyone help

I have a value for T1 and a value for T11 (which might be greater or
lesser.)

I want to fill T2 through T10 with a series of averages to smoothly fill the
gap so to speak.

So if T1 were 1 and T11 were 11, the series would count out 1 to 11
And if T1 were 22 and T2 were 2, then the series would count backwards from
22 to 2, even number only.

Anyone know how?