a(3)=43套系统:
{123} {1}{23} {1}{2}{3} {1}{2}{3}{12}
{2}{13} {12}{13}{23} {1}{2}{3}{13}
{3}{12} {1}{23}{123} {1}{2}{3}{23}
{2}{13}{123} {1}{2}{13}{23}
{3}{12}{123} {1}{2}{3}{123}
{1}{3}{12}{23}
{2}{3}{12}{13}
{1}{12}{13}{23}
{2}{12}{13}{23}
{3}{12}{13}{23}
{12}{13}{23}{123}
.
{1}{2}{3}{12}{13} {1}{2}{3}{12}{13}{23} {1}{2}{3}{12}{13}{23}{123}
{1}{2}{3}{12}{23} {1}{2}{3}{12}{13}{123}
{1}{2}{3}{13}{23} {1}{2}{3}{12}{23}{123}
{1}{2}{12}{13}{23} {1}{2}{3}{13}{23}{123}
{1}{2}{3}{12}{123} {1}{2}{12}{13}{23}{123}
{1}{2}{3}{13}{123} {1}{3}{12}{13}{23}{123}
{1}{2}{3}{23}{123} {2}{3}{12}{13}{23}{123}
{1}{3}{12}{13}{23}
{2}{3}{12}{13}{23}
{1} {2}{13}{23}{123}
{1}{3}{12}{23}{123}
{2}{3}{12}{13}{123}
{1}{12}{13}{23}{123}
{2}{12}{13}{23}{123}
{3}{12}{13}{23}{123}
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