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 A039991 Triangle of coefficients of cos(x)^n in polynomial for cos(nx). 18

%I

%S 1,1,0,2,0,-1,4,0,-3,0,8,0,-8,0,1,16,0,-20,0,5,0,32,0,-48,0,18,0,-1,

%T 64,0,-112,0,56,0,-7,0,128,0,-256,0,160,0,-32,0,1,256,0,-576,0,432,0,

%U -120,0,9,0,512,0,-1280,0,1120,0,-400,0,50,0,-1,1024,0,-2816,0,2816,0,-1232,0,220

%N Triangle of coefficients of cos(x)^n in polynomial for cos(nx).

%C Also triangle of coefficients of Chebyshev polynomials of first kind (T(n,x)) in decreasing order of powers of x. A053120 gives the coefficients in increasing order.

%C The polynomials R(n,x) := sum(a(n,m)*sqrt(x)^m, m=0..n) have g.f. (1-z)/(1 - 2*z + x*z^2) = ((1-z)/(1-2*z))/(1 - x*(-z^2/(1-2*z))) (from the row reversion of the g.f. of A053120 and x^2 -> x). Therefore this triangle becomes the Riordan triangle ((1-z)/(1-2*z), -z^2/(1-2*z)) if the vanishing columns are deleted (see A028297) and zeros are appended in each row numbered n>=1 in order to obtain a triangle. This is then A201701 with negative odd numbered columns. - _Wolfdieter Lang_, Aug 06 2014

%D M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 795.

%D Martin Aigner and Gunter M. Ziegler, Proofs From the Book, Springer 2004. See Chapter 18, Appendix.

%D E. A. Guilleman, Synthesis of Passive Networks, Wiley, 1957, p. 593.

%D Theodore J. Rivlin, Chebyshev polynomials: from approximation theory to algebra and number theory, 2. ed., Wiley, New York, 1990.

%H T. D. Noe, <a href="/A039991/b039991.txt">Table of n, a(n) for n = 0..5150</a>

%H M. Abramowitz and I. A. Stegun, eds., <a href="http://www.convertit.com/Go/ConvertIt/Reference/AMS55.ASP">Handbook of Mathematical Functions</a>, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].

%H <a href="/index/Ch#Cheby">Index entries for sequences related to Chebyshev polynomials.</a>

%F a(n, m) = 0 if n<m or m odd, (-1)^{m/2} if m=n is even, ((-1)^(3*m/2))*(2^(n-m-1))*n*binomial(n-1-m/2, n-1-m)/(n-m) else. a(n, m) = 2*a(n-1, m)-a(n-2, m-2), n >= 2, m >= 0; a(n, -2) := 0=: a(n, -1), a(0, 0)=1=a(1, 0).

%F G.f. for m-th column: 0 if m odd, (1-x)/(1-2*x) if m=0, else ((-1)^(m/2))*(x^m)*(1-x)/(1-2*x)^(m/2+1). For g.f. for row polynomials and row sums, see A053120.

%F G.f. row polynomials: (1-z)/(1 - 2*z + (x*z)^2. - _Wolfdieter Lang_, Aug 06 2014

%F Recurrence for the row polynomials Trev(n, x):= x^n*T(n, 1/x) = sum(a(n,m)*x^m, m=0..n): Trev(n, x) = 2*Trev(n-1, x) - x^2*Trev(n-2, x), n >= 1, Trev(-1, x) = 1/x^2 and Trev(0, x) = 1. From the T(n, x) recurrence. Compare this with A081265. - _Wolfdieter Lang_, Aug 07 2014

%e Letting c = cos x, we have: cos 0x = 1, cos 1x = 1c; cos 2x = 2c^2-1; cos 3x = 4c^3-3c, cos 4x = 8c^4-8c^2+1, etc.

%e From _Wolfdieter Lang_, Aug 06 2014: (Start)

%e The triangle a(n,m) begins:

%e n\m 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ...

%e 0: 1

%e 1: 1 0

%e 2: 2 0 -1

%e 3: 4 0 -3 0

%e 4: 8 0 -8 0 1

%e 5: 16 0 -20 0 5 0

%e 6: 32 0 -48 0 18 0 -1

%e 7: 64 0 -112 0 56 0 -7 0

%e 8: 128 0 -256 0 160 0 -32 0 1

%e 9: 256 0 -576 0 432 0 -120 0 9 0

%e 10: 512 0 -1280 0 1120 0 -400 0 50 0 -1

%e 11: 1024 0 -2816 0 2816 0 -1232 0 220 0 -11 0

%e 12: 2048 0 -6144 0 6912 0 -3584 0 840 0 -72 0 1

%e 13: 4096 0 -13312 0 16640 0 -9984 0 2912 0 -364 0 13 0

%e 14: 8192 0 -28672 0 39424 0 -26880 0 9408 0 -1568 0 98 0 -1

%e 15: 16384 0 -61440 0 92160 0 -70400 0 28800 0 -6048 0 560 0 -15 0

%e ...

%e --------------------------------------------------------------------------

%e Chebyshev T-polynomials (decreasing even or odd powers):

%e n=3: T(3, n) = 4*x^3 - 3*x^1; n=4: T(4, x) = 8*x^4 - 8*x^2 + 1. (End)

%p seq(seq(coeff(orthopoly[T](i,x),x,i-j),j=0..i),i=0..20); # _Robert Israel_, Aug 07 2014

%t row[n_] := CoefficientList[ ChebyshevT[n, x], x] // Reverse; Table[row[n], {n, 0, 11}] // Flatten(* _Jean-François Alcover_, Sep 14 2012 *)

%Y Cf. A028297 (without vanishing columns). A008310 (zero columns deleted then rows reversed).

%Y Triangle without zeros: A028297. Without signs: A081265.

%Y Cf. A053120 (increasing powers of x).

%K tabl,easy,sign,nice

%O 0,4

%A _David W. Wilson_

%E Entry improved by comments from _Wolfdieter Lang_, Jan 11 2000.

%E Edited: A053120 added in comment and crossrefs. Cfs. A028297 and A008310 specified. - _Wolfdieter Lang_, Aug 06 2014

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Last modified December 5 17:42 EST 2019. Contains 329768 sequences. (Running on oeis4.)