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Feb 14 at 23:51 comment added YCor Precisely, by induction, given $n\ge 2$, write $m=\lceil n/2\rceil$, and let $c_m$, $c_{n-m}$ be minimizing words on $m$ and $n-m\in\{m,m-1\}$ variables. Then $c_n(x_1,\dots,x_n)=[c_m(x_1,\dots,x_m),c_{n-m}(x_{m+1},\dots,x_n)]$ is minimizing, with $c_1(x_1)=x_1$. So $c_2(x,y)=[x,y]$, $c_3(x,y,z)=[[x,y],z]$, $c_4(\dots)=[[x,y],[z,w]]$, $c_5(\dots)=[[[x,y],z],[w,t]]$, etc., yields a minimizing sequence.
Feb 14 at 21:58 history edited Sean Eberhard CC BY-SA 4.0
Removed "not nested". They are nested!
Feb 14 at 19:30 history edited Sam Hopkins CC BY-SA 4.0
added 97 characters in body
Feb 14 at 19:26 vote accept Anton Petrunin
Feb 14 at 14:20 comment added Sean Eberhard @YCor Yes it is.
Feb 14 at 14:03 history edited LSpice CC BY-SA 4.0
Link to survey
Feb 14 at 12:32 comment added YCor So, is this oeis.org/A073121 ?
Feb 14 at 12:16 history answered Sean Eberhard CC BY-SA 4.0