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 A001760 Number of permutations of [n] with n-4 sequences. (Formerly M2176 N0870) 1
 2, 60, 836, 9576, 103326, 1106820, 12062152, 135391872, 1575253690, 19058801580, 240134763948, 3152151344088, 43098592576694, 613444153400340, 9082400109162224, 139747529003597424, 2232451845925297938 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 261. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS FORMULA From Barbara Haas Margolius (margolius(AT)math.csuohio.edu), Mar 12 2001: (Start) E.g.f.: (1/4)u(t)^4 + u(t)^3(-1-t/2) + u(t)^2(3+t) + (-7-t/2)u(t), where u(t) = sec(t) + tan(t), n>4. a(n) ~ n!(2/Pi)^(n + 3)/(3*Pi)(4n^3 + (24 - 3*Pi^2 - 12*Pi)n^2 + (13*Pi^2 + 44 + 3*Pi^3 - 36*Pi)n - 24*Pi + 16*Pi^2 - 9*Pi^3 + 24). (End) MAPLE u := t->sec(t)+tan(t); seq(i!*coeff(series((1/4)*u(t)^4+u(t)^3*(-1-t/2)+u(t)^2* (3+t)+(-7-t/2)*u(t), t, 35), t, i), i=5..24); # Barbara Haas Margolius (margolius(AT)math.csuohio.edu), Mar 12 2001 CROSSREFS Equals (1/3)*A001759(n+1)-(1/3)*(n-2)*A001758(n)-(2/3)*A001759(n). Sequence in context: A187626 A059934 A006333 * A230572 A157059 A272980 Adjacent sequences:  A001757 A001758 A001759 * A001761 A001762 A001763 KEYWORD nonn AUTHOR EXTENSIONS More terms from Barbara Haas Margolius (margolius(AT)math.csuohio.edu), Mar 12 2001 STATUS approved

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Last modified January 20 04:43 EST 2019. Contains 319323 sequences. (Running on oeis4.)