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 A220449 Define u(n) as in A220448; then a(1)=1, thereafter a(n) = u(n)*a(n-1). 5
 1, 1, -10, 10, 190, -730, -6620, 55900, 365300, -5864300, -28269800, 839594600, 2691559000, -159300557000, -238131478000, 38894192662000, -15194495654000, -11911522255750000, 29697351895900000, 4477959179352100000, -21683886333440500000, -2029107997508660900000, 15145164178973569000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The reason for including this sequence as well as A105750 is that the values of this sequence modulo various primes are of interest (see Moll). LINKS N. J. A. Sloane, Table of n, a(n) for n = 1..100 V. H. Moll, An arithmetic conjecture on a sequence of arctangent sums, 2012. See f_n. FORMULA A105750(n) = (-1)^(n+1)*a(n). Define x(n) as in A220447. Then x(n) = (a(n+1)+a(n))/((n+1)*a(n)). MAPLE x:=proc(n) option remember; if n=1 then 1 else (x(n-1)+n)/(1-n*x(n-1)); fi; end; f:=proc(n) option remember; global x; if n = 1 then 1 else n*x(n-1)*f(n-1)-f(n-1); fi; end; [seq(f(n), n=1..30)]; CROSSREFS Cf. A105750, A220446, A220447, A220448, A220450, A220451. Sequence in context: A047817 A065243 A105750 * A318968 A288051 A288504 Adjacent sequences:  A220446 A220447 A220448 * A220450 A220451 A220452 KEYWORD sign AUTHOR N. J. A. Sloane, Dec 22 2012 STATUS approved

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Last modified October 19 16:17 EDT 2019. Contains 328223 sequences. (Running on oeis4.)