A008964 Number of elements of order <= 2 in group of n X n upper triangular matrices over GF(2).

1, 2, 6, 28, 192, 1952, 28800, 618496, 19132416, 853508096, 54584672256, 5007197863936, 656391329021952, 122997864673574912, 32863344789678981120, 12522141669213840867328, 6792468641646224590503936, 5245768641385222636392415232

Offset

1,2

Links

Table of n, a(n) for n=1..18.

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 * A356577 A058128 A229112

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