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A024854 a(n) = s(1)t(n) + s(2)t(n-1) + ... + s(k)t(n-k+1), where k = [ n/2 ], s = (natural numbers), t = (natural numbers >= 3). 5
4, 5, 16, 19, 40, 46, 80, 90, 140, 155, 224, 245, 336, 364, 480, 516, 660, 705, 880, 935, 1144, 1210, 1456, 1534, 1820, 1911, 2240, 2345, 2720, 2840, 3264, 3400, 3876, 4029, 4560, 4731, 5320, 5510, 6160, 6370, 7084, 7315, 8096, 8349, 9200, 9476, 10400, 10700, 11700 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

LINKS

Table of n, a(n) for n=2..50.

Index entries for linear recurrences with constant coefficients, signature (1,3,-3,-3,3,1,-1).

FORMULA

a(n) = sum_{i=1..floor(n/2)} i*(n-i+3) = -floor(n/2)*(floor(n/2)+1)*(2*floor(n/2)-3n-8)/6. - Wesley Ivan Hurt, Sep 20 2013

G.f. -x^2*(-4-x+x^2) / ( (1+x)^3*(x-1)^4 ). - R. J. Mathar, Sep 25 2013

a(n) = 4*A058187(n-2)+A058187(n-3)-A058187(n-4). - R. J. Mathar, Sep 25 2013

a(n) = (4*n^3+21*n^2+14*n-9+3*(n^2+6*n+3)*(-1)^n)/48. - Luce ETIENNE, Nov 14 2014

MAPLE

seq(sum(i*(k-i+3), i=1..floor(k/2)), k=2..70); # Wesley Ivan Hurt, Sep 20 2013

MATHEMATICA

Table[-Floor[n/2] * (Floor[n/2] + 1) * (2 * Floor[n/2] - 3n - 8)/6, {n, 2, 100}] (* Wesley Ivan Hurt, Sep 20 2013 *)

CoefficientList[Series[- (- 4 - x + x^2)/((1 + x)^3 (x - 1)^4), {x, 0, 60}], x] (* Vincenzo Librandi, Oct 31 2014 *)

PROG

(MAGMA) [(4*n^3+21*n^2+14*n-9+3*(n^2+6*n+3)*(-1)^n)/48: n in [2..60]]; // Vincenzo Librandi, Oct 31 2014

CROSSREFS

Cf. A023855, A023856, A023857, A024305.

Sequence in context: A000695 A081345 A137527 * A025617 A227855 A078581

Adjacent sequences:  A024851 A024852 A024853 * A024855 A024856 A024857

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified August 16 23:58 EDT 2018. Contains 313809 sequences. (Running on oeis4.)