1.333, 1.5, 1.667, 1.75, 2, 3

I didn't find any sequence in a lookup, even for variations.
One remote database find was this "off the wall guess."

If n^(n + 2) + (n + 1)^(n + 3) is Prime, return (n+15)/12

Let's test it (using another program)

Table[If[PrimeQ[n^(n+2)+(n+1)^(n+3)],(n+15)/12.,],{n,21}]

{1.3333333333333333,,1.5,,1.6666666666666665,1.75, ,,2.,,,,,,,,,,,,3.}

Yeah. I know. it's a wild guess!!
The next two solutions would be 3.25, and 4.1666666666

Given the complexity of the prime test.. I'm impressed. Unfortunately, I
don't think this method will qualify as the "formula" Eric was looking for.

Rick

If I select the data table, another program I have converted it to the
following function.
However, it's not valid outside the range 1-6. It's just designed to remove
a lookup table.
I'm sure this is not what the op wanted either.

Function Fx(n)
Fx = (215376 Mod (n + 31)) / 12
End Function
'= = = = = = = = =

Sub TestIt()
Dim j
For j = 1 To 6
Debug.Print j; Fx(j)
Next j
End Sub

1 1.33333333333333
2 1.5
3 1.66666666666667
4 1.75
5 2
6 3
--
HTH :)
Dana DeLouis
Windows XP & Excel 2007

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