a(3)=32套系统:
{} {{1}} {{1}{12}} {{1}{12}{13}} {{1}{12}{13}{123}}
{{2}} {{1}{13}} {{2}{12}{23}} {{2}{12}{23}{123}}
{{3}} {{2}{12}} {{3}{13}{23}} {{3}{13}{23}{123}}
{{12}} {{2}{23}} {{1}{12}{123}}
{{13}} {{3}{13}} {{1}{13}{123}}
{{23}} {{3}{23}} {{2}{12}{123}}
{{123}} {{1}{123}} {{2}{23}{123}}
{{2}{123}} {{3}{13}{123}}
{{3}{123}} {{3}{23}{123}}
{{12}{123}}
{{13}{123}}
{{23}{123}}