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 A002020 a(n+1) = a(n) - n*(n-1)*a(n-1), with a(n) = 1 for n <= 3. (Formerly M3876 N1588) 5
 1, 1, 1, 1, -5, -17, 83, 593, -2893, -36101, 172195, 3421285, -15520165, -467129785, 1954015955, 86971636825, -323371713725, -21196564551725, 66760541581475, 6552909294409325, -16279195926455125, -2506384727801998625, 4330877561309153875 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 REFERENCES R. Kelisky, The numbers generated by exp(arctan x), Duke Math. J., 26 (1959), 569-581. 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 T. D. Noe, Table of n, a(n) for n = 0..100 MAPLE f := proc(n) option remember; if n<=3 then 1 else f(n-1)-(n-1)*(n-2)*f(n-2); fi; end; MATHEMATICA t = {1, 1, 1, 1}; Do[AppendTo[t, t[[-1]] - (n-1) (n - 2) t[[-2]]], {n, 4, 20}] (* T. D. Noe, Aug 30 2012 *) CROSSREFS Sequence in context: A149753 A149754 A149755 * A038183 A149756 A036756 Adjacent sequences:  A002017 A002018 A002019 * A002021 A002022 A002023 KEYWORD sign,easy AUTHOR STATUS approved

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Last modified October 14 05:08 EDT 2019. Contains 327995 sequences. (Running on oeis4.)