6,2

J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969.

I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p, 99.

M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351.

Sequence in context: A028385 A138762 A139777 this_sequence A079230 A111887 A015341

Adjacent sequences: A015324 A015325 A015326 this_sequence A015328 A015329 A015330

nonn,easy

Olivier Gerard (ogerard(AT)ext.jussieu.fr)