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 A007836 Springer numbers associated with symplectic group. 3
 1, 1, 1, 5, 23, 151, 1141, 10205, 103823, 1190191, 15151981, 212222405, 3242472023, 53670028231, 956685677221, 18271360434605, 372221031054623, 8056751598834271, 184647141575344861, 4466900836910758805 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Comments from F. Chapoton, Oct 30 2009: To compute this sequence, I used something similar to the Boustrophedon definition of the Euler numbers, but with two triangles instead of one. This is described (page 94) in Arnold's article in "Lecons de mathematiques d'aujourd'hui, volume 1" Editions Cassini. This is very similar to A001586, except that the initial conditions ( (0,1) at top of the two triangles ) are exchanged. REFERENCES V. I. Arnold, The calculus of snakes and the combinatorics of Bernoulli, Euler and Springer numbers of Coxeter groups, Uspekhi Mat. Nauk., 47 (#1, 1992), 3-45 = Russian Math. Surveys, Vol. 47 (1992), 1-51. V. I. Arnold, Nombres d'Euler, de Bernoulli et de Springer pour les groupes de Coxeter et les espaces de morsification : le calcul des serpents, in "Lecons de mathematiques d'aujourd'hui, volume 1", Editions Cassini. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 F. Chapoton, Sage program Michael E. Hoffman, Derivative Polynomials, Euler Polynomials, and Associated Integer Sequences M. Josuat-Verges, J.-C. Novelli and J.-Y. Thibon, The algebraic combinatorics of snakes, arXiv preprint arXiv:1110.5272, 2011 A. Vieru, Agoh's conjecture: its proof, its generalizations, its analogues, arXiv preprint arXiv:1107.2938, 2011. FORMULA a(m) = P_n(1) - Q_n(1) (see A155100 and A104035), defining Q_{-1} = 0. Cf. A156142. MATHEMATICA p[n_, u_] := D[Tan[x], {x, n}] /. Tan[x] -> u /. Sec[x] -> Sqrt[1+u^2] // Expand; p[-1, u_] = 1; t[n_, k_] := t[n, k] = k*t[n-1, k-1]+(k+1)*t[n-1, k+1]; t[0, 0] = 1; t[0, _] = 0; t[-1, _] = 0; q[n_, u_] := Sum[t[n, k]*u^k, {k, 0, n}]; a[n_] := p[n, 1]-q[n, 1]; a[0]=1; Table[a[n], {n, 0, 19}] (* Jean-François Alcover, Feb 05 2014 *) CROSSREFS Cf. A001586, A155100, A104035, A156142. Sequence in context: A047049 A020034 A128884 * A233568 A157306 A306185 Adjacent sequences:  A007833 A007834 A007835 * A007837 A007838 A007839 KEYWORD nonn,nice AUTHOR EXTENSIONS More terms from F. Chapoton, Oct 30 2009 STATUS approved

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Last modified January 29 16:58 EST 2020. Contains 331347 sequences. (Running on oeis4.)