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: A050998 A128484 A116463 this_sequence A109690 A013905 A132905

Adjacent sequences: A015328 A015329 A015330 this_sequence A015332 A015333 A015334

nonn,easy

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