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A301417
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Sums of positive coefficients in generalized Chebyshev polynomials of the first kind, for a family of 4 data.
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6
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1, 4, 19, 98, 516, 2725, 14400, 76105, 402229, 2125864, 11235643, 59382770, 313850616, 1658767513, 8766940464, 46335152161, 244891172089, 1294302130684, 6840663104371, 36154365042098, 191083538489436, 1009917298758493, 5337628549243344, 28210506508524169
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OFFSET
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1,2
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COMMENTS
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Re-express the Girard-Waring formulae to yield the mean powers in terms of the mean symmetric polynomials in the data values. Then for a family of 4 data, the sum of the positive coefficients in these polynomials is a(n). a(n+1)/a(n) approaches 1/(2^(1/4)-1). (For a family of 2 data, the coefficients of these polynomials give the Chebyshev polynomials of the first kind.)
More precisely, given a finite collection X:=(x(i), i =1..n) of data, the Girard-Waring formulae express the sum of the k-th powers of the data, S_k(X):=Sum(x(i)^k, i=1..n), in terms of the elementary symmetric polynomials in the data. The j-th elementary symmetric polynomial is s_j(X):=Sum(Product(x(i), x(i) in X_0), X_0 \subseteq X, where |X_0|=j). So the Girard-Waring formulae provide coefficients a(J,k) such that S_k(X)=Sum(a(J,k)*Product(s_j(X), j \in J), J:=(j(1), j(2), ...) where j(1)+j(2)+...=k). [Thus J is an integer partition of k.] By "mean powers" I mean T_k(X):=Sum(x(i)^k, i=1..n)/n. By the "mean symmetric polynomials" I mean t_j(X):=s_j(X)/binomial(n,j). The Girard-Waring mean formulae then provide coefficients b(J,k,n) such that T_k(X)=Sum(b(J,k,n)*Product(t_j(X), j in J), J:=(j(1), j(2), ...) where j(1)+j(2)+...=k). So the sums of positive coefficients that I reference, for a fixed data set size n, and a fixed power k, are Sum(b(J,k,n), J:=(j(1), j(2), ...) where j(1)+j(2)+...=k, such that b(J,k,n)>0).
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LINKS
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Gregory Gerard Wojnar, Java program. Within the program, the variable I denotes the number of data; J denotes the exponent.
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FORMULA
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G.f.: (-x*(x+1)^3+1)/(x^5+3*x^4+2*x^3-2*x^2-5*x+1); this denominator equals (1-x)*(2-(1+x)^4).
a(n+5) = 5*a(n+4)+2*a(n+3)-2*a(n+2)-3*a(n+1)-a(n).
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MATHEMATICA
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CoefficientList[Series[(-x (x + 1)^3 + 1)/(x^5 + 3 x^4 + 2 x^3 - 2 x^2 - 5 x + 1), {x, 0, 23}], x] (* Michael De Vlieger, Apr 07 2018 *)
LinearRecurrence[{5, 2, -2, -3, -1}, {1, 4, 19, 98, 516}, 24] (* Jean-François Alcover, Dec 02 2018 *)
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PROG
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(PARI) lista(4, nn) \\ use pari script link; Michel Marcus, Apr 21 2018
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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