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A014489 Positions of involutions (permutations whose square is the identity) in reverse colexicographic order (A055089/A195663). 3
0, 1, 2, 5, 6, 7, 14, 16, 21, 23, 24, 25, 26, 29, 54, 55, 60, 67, 80, 82, 86, 94, 105, 107, 111, 119, 120, 121, 122, 125, 126, 127, 134, 136, 141, 143, 264, 265, 266, 269, 288, 289, 314, 316, 339, 341, 390, 391, 396, 403, 414, 415, 444, 450, 469 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Robert Israel, Table of n, a(n) for n = 0..3996

MAPLE

N:= 100: # to get a(0) to a(N)

M:= 0: A[0]:= 0: count:= 0:

for m from 2 while count < N do

  P:= remove(t -> t[1]=1, combinat:-permute(m));

  P:= map(t -> ListTools:-Reverse(subs([seq(i=m+1-i, i=1..m)], t)), P);

  R:= select(t -> max(map(nops, convert(P[t], disjcyc))) = 2, [$1..nops(P)]);

  for r in R do

     count:= count+1;

     A[count]:= r+M;

     if count = N then break fi;

  od:

  M:= M + nops(P);

od:

seq(A[i], i=0..count); # Robert Israel, Oct 28 2015

CROSSREFS

Positions of zeros in A261099.

From a(1)=1 onward also positions of 2's in A055092.

Subsequences: A060112, A064640.

Cf. A055089, A195663.

Cf. also A261220.

Sequence in context: A117548 A175135 A244314 * A286270 A033959 A167455

Adjacent sequences:  A014486 A014487 A014488 * A014490 A014491 A014492

KEYWORD

nonn

AUTHOR

Wouter Meeussen

EXTENSIONS

Name changed by Antti Karttunen, Aug 30 2015

STATUS

approved

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Last modified February 18 20:32 EST 2018. Contains 299330 sequences. (Running on oeis4.)