$${\begin{array}{l} 3^2 = 9 \\ ({3^2})^2 = 3^4 = 81 \\ ({3^4})^2 = 3^8 = 6561 \\ ({3^8})^2 = 3^{16} = 43 \, 046 \, 721 \\ ({3^{16}})^2 = 3^{32} = 1 \, 853 \, 020\, 188\, 851\, 841 \\ ({3^{32}})^2 = 3^{64} = 3 \, 433\, 683\, 820\, 292\, 512\, 484\, 657\, 849\, 089\, 281 \end{array}}$$