4,2

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: A004948 A138063 A122715 this_sequence A028484 A057699 A033525

Adjacent sequences: A015288 A015289 A015290 this_sequence A015292 A015293 A015294

nonn,easy

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