**Update:** To generate a list of spheres similar to the circles in OP (sphere `k` just touching sphere `k-2`):

    ClearAll[tr]
    tr[n_] := (2 n^2  + (-1)^n)/4;

    Graphics[Circle[{tr @ #, 0}, #] & /@ Range[10]]
[![enter image description here][1]][1]

    Graphics3D[{Opacity[.5], Sphere[{tr @ #, 0, 0}, #] & /@ Range[10]}, Boxed -> False]
[![enter image description here][2]][2]

**Original answer:**

You can use [`Translate`](https://reference.wolfram.com/language/ref/Translate.html) and [`Scale`](https://reference.wolfram.com/language/ref/Scale.html) `Sphere[]` as follows:

    radii = Range[5];

    Graphics3D[Translate[Scale[Sphere[], #], {#^2, 0, 0}] & /@ radii]
[![enter image description here][3]][3]

or translate to leave gaps between spheres:

    translations = 2 Accumulate[radii];

    Graphics3D[MapThread[Translate[Scale[Sphere[], #], {#2, 0, 0}] &, {radii, translations}]]

[![enter image description here][4]][4]


  [1]: https://i.sstatic.net/gXosW.png
  [2]: https://i.sstatic.net/a998N.png
  [3]: https://i.sstatic.net/B03CX.png
  [4]: https://i.sstatic.net/U0Skq.png