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: A002606 A047637 A123099 this_sequence A103537 A136928 A013538

Adjacent sequences: A015321 A015322 A015323 this_sequence A015325 A015326 A015327

nonn,easy

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