The a(3) = 36 set-systems:
{{1}{2}{3}} {{12}{13}{23}{123}} {{2}{3}{12}{13}{23}}
{{12}{13}{23}} {{1}{2}{3}{12}{13}} {{2}{3}{12}{13}{123}}
{{1}{2}{3}{12}} {{1}{2}{3}{12}{23}} {{2}{12}{13}{23}{123}}
{{1}{2}{3}{13}} {{1}{2}{3}{13}{23}} {{3}{12}{13}{23}{123}}
{{1}{2}{3}{23}} {{1}{2}{12}{13}{23}} {{1}{2}{3}{12}{13}{23}}
{{1}{2}{13}{23}} {{1}{2}{3}{12}{123}} {{1}{2}{3}{12}{13}{123}}
{{1}{2}{3}{123}} {{1}{2}{3}{13}{123}} {{1}{2}{3}{12}{23}{123}}
{{1}{3}{12}{23}} {{1}{2}{3}{23}{123}} {{1}{2}{3}{13}{23}{123}}
{{2}{3}{12}{13}} {{1}{3}{12}{13}{23}} {{1}{2}{12}{13}{23}{123}}
{{1}{12}{13}{23}} {{1}{2}{13}{23}{123}} {{1}{3}{12}{13}{23}{123}}
{{2}{12}{13}{23}} {{1}{3}{12}{23}{123}} {{2}{3}{12}{13}{23}{123}}
{{3}{12}{13}{23}} {{1}{12}{13}{23}{123}} {{1}{2}{3}{12}{13}{23}{123}}
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