2,2

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.

G.f.: 1/[(1-x)(1+7x)(1-49x)].

Sequence in context: A022220 A009987 A076572 this_sequence A130014 A015323 A145315

Adjacent sequences: A015255 A015256 A015257 this_sequence A015259 A015260 A015261

nonn,easy

Olivier Gerard (olivier.gerard(AT)gmail.com)