0,3

A. C. Aitken, On the number of distinct terms in the expansion of symmetric and skew determinants, Edinburgh Math. Notes, No. 34 (1944), 1-5.

A. Cayley, On the number of distinct terms in a symmetrical or partially symmetrical determinant, Collected Mathematical Papers. Vols. 1-13, Cambridge Univ. Press, London, 1889-1897, Vol. 9, p. 190.

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 260, #12, a_n.

P. A. MacMahon, Combinations derived from m identical sets of n different letters and their connexion with general magic squares, Proc. London Math. Soc., 17 (1917), 25-41.

Problem E2297, Amer. Math. Monthly, 79 (1972), 519-520.

R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Example 5.2.9 and Problem 5.22.

T. D. Noe, Table of n, a(n) for n=0..100

E.g.f.: (1-x)^(-1/2)*exp(x/2+x^2/4). a(n+1) = (n+1)*a(n) - binomial(n, 2)*a(n-2) - Comtet.

Cf. A059422, A059423, A059424.

Sequence in context: A007779 A084161 A102038 this_sequence A007868 A136726 A112831

Adjacent sequences: A002132 A002133 A002134 this_sequence A002136 A002137 A002138

nonn,nice,easy

njas