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 A112742 a(n) = n^2*(n^2-1)/3. 6
 0, 0, 4, 24, 80, 200, 420, 784, 1344, 2160, 3300, 4840, 6864, 9464, 12740, 16800, 21760, 27744, 34884, 43320, 53200, 64680, 77924, 93104, 110400, 130000, 152100, 176904, 204624, 235480, 269700, 307520, 349184, 394944, 445060, 499800, 559440 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Second derivative of the n-th Chebyshev polynomial (of the first kind) evaluated at x=1. The second derivative at x=-1 is just (-1)^n * a(n). The difference between two consecutive terms generates the sequence a(n+1)-a(n) = A002492(n). Consider the partitions of 2n into two parts (p,q) where p <= q. Then a(n) is the total volume of the family of rectangular prisms with dimensions p, |q-p| and |q-p|. - Wesley Ivan Hurt, Apr 15 2018 LINKS Eric Weisstein's World of Mathematics, Chebyshev polynomials of the first kind Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA a(n) = (n-1)*n^2*(n+1)/3 = 4*A002415(n). a(n) = 2*( A000914(n-1) + C(n+1,4) ) - David Scambler, Nov 27 2006 a(n) = 5*a(n-1)-10*a(n-2)+10*a(n-3)-5*a(n-4)+a(n-5). G.f.: 4*x^2*(1+x)/(1-x)^5. - Colin Barker, Jan 26 2012 EXAMPLE a(4)=80 because: C_4(x) = 1 - 8x^2 + 8x^4 C'_4(x) = -16x+32x^3 C''_4(x) = -16+96x^2 C''_4(1) = -16+96 = 80 MATHEMATICA Table[D[ChebyshevT[n, x], {x, 2}], {n, 0, 100}] /. x -> 1 PROG (PARI) a(n)=n^2*(n^2-1)/3 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Cf. A000914, A002415, A002492. Sequence in context: A199904 A250132 A025220 * A158494 A209456 A069145 Adjacent sequences:  A112739 A112740 A112741 * A112743 A112744 A112745 KEYWORD nonn,easy AUTHOR Matthew T. Cornick (maruth(AT)gmail.com), Sep 16 2005 STATUS approved

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Last modified January 19 17:45 EST 2019. Contains 319309 sequences. (Running on oeis4.)