OFFSET
3,1
LINKS
Sean A. Irvine, Table of n, a(n) for n = 3..100
FORMULA
a(n) = (n^4+6*n^3+11*n^2-12*n+6)/6 (conjectured). - Giovanni Resta, Jun 08 2015
Conjectured g.f.: (-2-5x+3x^2+x^3-x^4)/(-1+x)^5. - Benedict W. J. Irwin, Feb 20 2016
MATHEMATICA
a[n_] := Block[{s, allb, r = Flatten[Table[{i, j}, {i, n}, {j, i + 1, n}], 1]}, allb[pp_] := Union@ Table[ s=pp; s[[Range @@ e]] = Reverse[ s[[ Range @@ e]]]; s, {e, r}]; Length[Flatten[allb /@ allb[Range[n]], 1] // Union] - 1]; a /@ Range[3, 15] (* Giovanni Resta, Jun 08 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(9)-a(41) from Giovanni Resta, Jun 08 2015
STATUS
approved