<p>Ordering and enumeration of the <a href="https://en.wikipedia.org/wiki/Bell_number" class="extiw" title="w:Bell number">15</a> <a href="https://en.wikipedia.org/wiki/Partition_of_a_set" class="extiw" title="w:Partition of a set">partitions</a> of a 4-element set
</p><p>The binary matrix on the right is in <a href="https://en.wikipedia.org/wiki/colexicographic_order" class="extiw" title="w:colexicographic order">colexicographic order</a>.<br>
Read as reverse binary these are the numbers <span style="white-space:nowrap"><a href="https://en.wikipedia.org/wiki/On-Line_Encyclopedia_of_Integer_Sequences" title="Sloane's"><img alt="Sloane's" src="https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/OEISicon_light.svg/11px-OEISicon_light.svg.png" decoding="async" width="11" height="15" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/OEISicon_light.svg/17px-OEISicon_light.svg.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/OEISicon_light.svg/22px-OEISicon_light.svg.png 2x" data-file-width="409" data-file-height="556"></a> <a href="//oeis.org/A231428" class="extiw" title="oeis:A231428">A231428</a></span>(1..15) = 0, 1, 2, 4, 7, 8, 12, 16, 18, 25, 32, 33, 42, 52, 63.
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