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A014489 Positions of involutions (permutations whose square is the identity) in reverse colexicographic order (A055089/A195663).

%I A014489 #16 Nov 07 2015 08:33:46
%S A014489 0,1,2,5,6,7,14,16,21,23,24,25,26,29,54,55,60,67,80,82,86,94,105,107,
%T A014489 111,119,120,121,122,125,126,127,134,136,141,143,264,265,266,269,288,
%U A014489 289,314,316,339,341,390,391,396,403,414,415,444,450,469
%N A014489 Positions of involutions (permutations whose square is the identity) in reverse colexicographic order (A055089/A195663).
%H A014489 Robert Israel, <a href="/A014489/b014489.txt">Table of n, a(n) for n = 0..3996</a>
%p A014489 N:= 100: # to get a(0) to a(N)
%p A014489 M:= 0: A[0]:= 0: count:= 0:
%p A014489 for m from 2 while count < N do
%p A014489   P:= remove(t -> t[1]=1, combinat:-permute(m));
%p A014489   P:= map(t -> ListTools:-Reverse(subs([seq(i=m+1-i,i=1..m)],t)),P);
%p A014489   R:= select(t -> max(map(nops,convert(P[t],disjcyc))) = 2, [$1..nops(P)]);
%p A014489   for r in R do
%p A014489      count:= count+1;
%p A014489      A[count]:= r+M;
%p A014489      if count = N then break fi;
%p A014489   od:
%p A014489   M:= M + nops(P);
%p A014489 od:
%p A014489 seq(A[i],i=0..count); # _Robert Israel_, Oct 28 2015
%Y A014489 Positions of zeros in A261099.
%Y A014489 From a(1)=1 onward also positions of 2's in A055092.
%Y A014489 Subsequences: A060112, A064640.
%Y A014489 Cf. A055089, A195663.
%Y A014489 Cf. also A261220.
%K A014489 nonn
%O A014489 0,3
%A A014489 _Wouter Meeussen_
%E A014489 Name changed by _Antti Karttunen_, Aug 30 2015