Presumably the sum $S_m$ can be given in a more compact way as $S_m = 2\sum_{k=1}^{m-1} \frac{3^k} {2^{2^k}}.$ The limit should be a transcendental number, since the sum is extremely lacunary, so it seems unlikely that a closed for exists...
Igor Rivin
- 96.4k
- 11
- 153
- 366