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 A008964 Number of elements of order <= 2 in group of n X n upper triangular matrices over GF(2). 0
 1, 2, 6, 28, 192, 1952, 28800, 618496, 19132416, 853508096, 54584672256, 5007197863936, 656391329021952, 122997864673574912, 32863344789678981120, 12522141669213840867328, 6792468641646224590503936, 5245768641385222636392415232 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS I. M. Isaacs and Dikran B. Karagueuzian, Involutions and characters of upper triangular matrix groups, Math. Comp., 74 (2005), 2027-2033. FORMULA a(n) = Sum_{r=0..floor(n/2)} f(n, r) where f(n, 0) = 1, f(1, r) = 0, f(n, r) = 2^r * f(n - 1, r) + (2^(n-r) - 2^(r-1)) * f(n - 1, r - 1). - Sean A. Irvine, Apr 15 2018 CROSSREFS Sequence in context: A231621 A084870 A111342 * A058128 A229112 A201959 Adjacent sequences:  A008961 A008962 A008963 * A008965 A008966 A008967 KEYWORD nonn AUTHOR Dikran Karagueuzian (dikran(AT)math.wisc.edu) EXTENSIONS More terms from Sean A. Irvine, Apr 15 2018 STATUS approved

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Last modified August 7 08:08 EDT 2020. Contains 336274 sequences. (Running on oeis4.)